Sensor-synchronized spectrally-structured-light imaging

ABSTRACT

A spectral imaging device is configured to capture color images synchronized with controlled illumination from different color light emitting diodes. A processor in the device applies a coupling factor to sampled color images to convert sampled pixels into spectral channels corresponding to LED color and color filter. Multi-spectral spectricity vectors produced at pixel locations are used along with spatial information to classify objects, such as produce items.

RELATED APPLICATION DATA

This application is a continuation of Ser. No. 14/201,852, filed Mar. 8,2014 (now U.S. Pat. No. 9,593,982), which is a continuation-in-part ofSer. No. 13/840,451, filed Mar. 15, 2013 (now U.S. Pat. No. 9,060,113),which is a non-provisional of co-pending provisional applications61/688,722, filed May 21, 2012, and 61/706,982, filed Sep. 28, 2012.Application Ser. No. 14/201,852 also claims priority to provisionalapplication 61/906,886, filed Nov. 20, 2013, and provisional application61/907,362, filed Nov. 21, 2013, both with same title. These patents andapplications are hereby incorporated by reference into thisspecification.

REFERENCE TO COMPUTER PROGRAM LISTING APPENDIX

This application includes a computer program listing appendix includingthe following Matlab computer program files:Spectricityv11_multiday_set2-code_appendix.txt (created on Nov. 19,2013, file size of 33069 bytes), SpectraImg -code_appendix.txt (createdon Nov. 18, 2013, file size of 9425 bytes) and spectraId-code_appendix.txt (created on Nov. 18, 2013, file size of 9233 bytes),configParser -code_appendix.txt (created on Nov. 18, 2013, file size of1370 bytes), ClassifierTSVQ_appendix.txt (created on Mar. 7, 2014, filesize of 7442 bytes), basicClassify_appendix.txt (created on Mar. 7,2014, file size of 4386 bytes), and VQ_appendix.txt (created on Mar. 7,2014, file size of 3759 bytes), all incorporated into thisspecification.

TECHNICAL FIELD

The present technology concerns, e.g., imaging spectrometry.

BACKGROUND AND INTRODUCTION OF THE TECHNOLOGY

Both natural light (‘ambient’) photography and flash-assisted (readbroadly: ‘human assisted light supplementation’) photography have beenaround since the Daguerreotype. The present technology concerns howprimarily the latter form of lighting, call it ‘flash’ for conciseness,can be so designed and implemented as to effectively qualify it withinthe general art of ‘imaging spectrometry’ or ‘hyper-spectral imaging.’

In a nutshell, by illuminating a scene with several different brief(frame-synchronized) ‘spectrally structured’ light sources, even acommon Bayer pattern CMOS camera can effectively become an imagingspectrometer with ‘N bands,’ N in very early days being practically onthe order of 5 to 10 bands, but with fine prospects of going higher,especially as design principles behind Bayer patterns (and RGBW, e.g.,from Sony) are reconsidered in light of this technology.

An introduction of the technology must make note of multi-chip LEDs (seee.g. Edison's 2012-era Federal FM series, depicted in FIG. 7) as beingat least a seed for just what the doctor ordered regarding ‘spectrallystructured light.’ A core idea—and current preferred embodiment—is tosynchronize pulsing of different LED light sources with individualframes of a CMOS sensor, thereby creating the informational basis forN-band imaging. Light sources other than LEDs can certainly beconsidered but by 2012 standards, multi-chip and/or ‘dual’ LEDs areleading candidates to realize this technology.

A particularly intriguing choice of ‘bands’ is the 3 very well-known1931 CIE color matching functions and/or their orthogonally transformedfunctions. With such choices, the stage is set for taking thebeyond-religiously-fervent universe of color photography to itsmultiverse destiny: blandly referred to as ‘direct chromaticity capture’in this disclosure.

The bulk of this disclosure zooms in on the design principles andphysical realizations of turning virtually any electronic imaging sensorinto an imaging spectrometer via specific coordination with somesupplemental light source. With the core ‘how’ then elucidated, fouressentially discrete applications will be presented and described,including A) the niche application of hyper-spectral imaging, B) themedical imaging potential of this technology, C) the previouslyalluded-to culturally-volatile topic of radically improved colorphotography for both ‘digital cameras’ and smart phones (as 2012 stilldraws pretty sharp lines between the two), and D) uses of N-band imagingwithin the mature technology of digital watermarking and ‘imagefingerprinting.’

Subsequent to the initial disclosure, this disclosure has been expandedsignificantly in several areas, including:

-   -   methods and systems for classifying and recognizing various        types of objects;    -   such systems employing various imaging configurations, with        various options on spectral light sources, optical filters,        polarimetric sensing, sensing of these spectral and polarimetric        pixel samples at 3 spatial dimensions (including plenoptic        sensing and Kinect 3D structure sensing), scanning techniques,        and synchronizing controlled capture under various lighting and        sensing states;    -   training and applying classifiers for particular fields,        including produce identification, produce ripening;    -   advances in illumination, sensing and post processing to address        various environmental effects, including specular reflections,        product package layers (e.g., plastic packaging or bags that        hamper object identification); and    -   advances in sensing and post processing, prior to training and        applying a classifier to obtain vectors per pixel, that combine        spectral, polarimetric, and spatial relationships among pixel        elements.

Many more system configurations, lighting and sensing devices, and pixelpost processing techniques and device configurations are detailedfurther below. A myriad of inventive combinations of these and otheraspects of the disclosure are contemplated and not limited to theparticular example embodiments. We provide source code samples asexamples. It is contemplated that the various signal processingdescribed may be implemented as software instructions for execution ongeneral purpose computing devices or special purpose processors,including devices with DSPs, GPUs, etc. These software instructions maybe ported into processor device specific firmware versions, ASICs,FPGAs, etc. in various combinations, as well as leverage cloud computingservices for execution (particular for training, classifying andrecognition services).

The foregoing and other features and advantages of the presenttechnology will be more readily apparent from the following DetailedDescription, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 illustrates how most modern cameras distinguish red apples fromgreen apples.

FIG. 2 presents a plot of three spectral detection profiles of anillustrative Bayer-pattern CMOS sensor.

FIG. 3 is similar to FIG. 1, but includes information about an idealizedspectral reflectance profile of a green apple, and of a red apple.

FIG. 4 introduces an idealized ambient lighting source spectral curve.

FIG. 5 presents a case involving slight green-ish, mainly blue-ishillumination.

FIG. 6 shows how an apple may be mis-colored when rendered on a screen,due to illumination.

FIGS. 7 and 8 introduce the notion of multi-colored flash.

FIG. 9 is similar to FIG. 5, but incorporating insight from FIG. 8.

FIG. 10 shows another family of spectral curves.

FIG. 11 illustrates different spectral samplings of an apple.

FIG. 12 illustrates how data gathered in FIG. 11 can be used to producespectral information for the apple.

FIG. 13 shows a linear function estimation arrangement that can be usedwith the spectral information of FIG. 12.

FIGS. 14-17 show the evolution from a five-band rectangular solution setto a linear algebra representation of the spectral data.

FIG. 18 introduces some of the considerations from a sensor side of thesystem.

FIGS. 19-22 delve into considerations concerning the illumination LEDs.

FIG. 23 illustrates a relationship between Bayer filters and orthogonalcolor matching functions.

FIG. 24 details use of a CIE matrix to generate chromaticitycoordinates.

FIG. 25 shows how the present technology resolves an apple's color toparticular coordinates on a chromaticity diagram.

FIG. 26 delves further into ambient illumination combined with the LEDillumination.

FIG. 27 illustrates uses of the technology in medical applications.

FIG. 28 introduces use of the technology in food safety, iteminspection, and anti-counterfeiting applications.

FIG. 29 illustrates use of the technology in digital watermarking andrelated applications.

FIG. 30 details how conventional form-factor flash units can employ thepresent technology.

FIGS. 31 and 31A illustrate an implementation using a clip-onillumination accessory.

FIG. 32 addresses aspects of the technology concerning motion.

FIGS. 33-36 further elaborate considerations involving ambient lighting.

FIG. 37 details how unknown ambient lighting spectral coefficients canbe removed from aggregate mathematical equations.

FIG. 38 is a diagram illustrating a process of generating spectralimages in response to pulsing a target object with illumination in thepresence of ambient light.

FIG. 39 depicts a matrix with the color channels of the sensor, R, G andB, on the vertical axis, and the LED light source colors on thehorizontal axis, B, G, R, A, Y.

FIG. 40 illustrates a method for determining coupling factors for a pairof light sources and image sensor.

FIGS. 41-42 illustrate spectra measurements of LEDs used in various ofour experiments.

FIG. 43 illustrates chromaticity errors caused by an RGB camera.

FIG. 44 depicts that an incident beam of light (e.g., from a focusedLED) generally gives rise to specular and diffuse reflection.

FIG. 45 is a diagram illustrating an example of how much light from oneangle, Wi, gets reflected into another reflectance angle Wr.

FIGS. 46, 47 and 48 provide visible examples of the field anglenon-uniformities.

FIG. 46 depicts green LED differential lighting of some white papersheets.

FIG. 47 depicts the same scene as FIG. 46, but now differentially lit bya blue LED one frame in a video sequence later, where the pulsing of theLEDs are coordinated with the framing of a camera—a Bayer-pixel colorcamera in this case.

FIG. 48 depicts an iso-spectricity overlay image of the white sheets ofpaper, each separately illuminated by the 5 LEDs.

FIG. 49 contains a summary of largely what FIGS. 46-48 have shownexperimentally, followed by further figures and explanations of boththeoretical procedures and actual calibration procedures that can beperformed to mitigate these errors.

FIG. 50 provides an illustration that explains a process of fieldcorrection.

FIG. 51 depicts spectricity errors caused by gross reflectance values(i.e. lightness-darkness of surfaces).

FIG. 52 depicts reflectance-level spectricity vector correction.

FIG. 53 depicts an image of a scene taken with a normal Bayer-type colorcamera.

FIG. 54 depicts an image of the same scene as FIG. 53 but with theambient light significantly dimmed.

FIG. 55 is an image obtained from the same ambient lit scene as FIG. 54but now with the ‘differential tweak’ of the blue LED turned on.

FIG. 56 is an image obtained from the same ambient lit scene as FIG. 54but now with the ‘differential tweak’ of the green LED turned on.

FIG. 57 depicts the sum total of the increases in pixel values measuredfor each of the 5 LED-ambient images (their raw digital number increasesacross R, G and B values), displayed as a black and white image.

FIGS. 58-60 illustrate an application of N-D spectral vectors toidentify ripeness of produce.

FIG. 61 illustrates an example of a strong classifier.

FIG. 62 illustrates an example of a weak classifier.

FIG. 63 is a diagram illustrating an image sensor comprising an array ofpixel elements.

FIG. 64 is a diagram illustrating top and perspective views of an imagesensor with optical band pass filters, each for a band of wavelengthsλ_(n) (n being a number representing a band of wavelengths), arranged onan array of pixel elements.

FIG. 65 is a diagram illustrating top and perspective views of an imagesensor with a polarizer (e.g., for measuring one of four orientations 0,45, 90 and 135 degrees) over each pixel element.

FIG. 66 is a diagram illustrating top and perspective views of an imagesensor with a polarizer per pixel element, and optical band pass filterper 2D block of pixel elements.

FIG. 67 is a diagram illustrating a side view of an image sensor andlens configuration, together forming a plenoptic camera.

FIG. 68 is a diagram illustrating a side view of an image sensor havingoptical band pass filters on the sensor, followed by a microlens array,where the filters are positioned to coincide with a correspondingmicrolens array element such that there is one filter per sub-imageobtained through the positioning of a main lens relative to themicrolens array as shown.

FIG. 69 is a diagram illustrating a side view of an image sensor likethe one in FIG. 68, but further adding a layer of polarizers between theoptical filter elements and microlens array.

FIG. 70 is a diagram illustrating a side view of an image sensor likethe one in FIG. 68, but with the alternative of having multiple opticalband pass filters per sub-image.

FIG. 71 is a diagram illustrating a side view of an image sensor likethe one in FIG. 69, but without the optical band pass filters.

The following provides additional descriptions of selected figures:

FIG. 1 shows, at 70, a classic “Bayer Pattern,” typifying the colorfilter arrangements of the individual pixels of a modern CMOS camera.Below is shown part of a 2012-era smartphone 40, with a CMOS cameraaperture 50, and an LED flash aperture 60. Also shown are two apples, ared apple 20 and a green apple 30, respectively reflecting red and greenlight from the sun 10 (which produces “white light” ambientillumination).

FIG. 3 shows how the spectral reflectance profile, 90, of the greenapple might nicely mimic the Bayer-pixel spectral profile of the “G”channel. In the lower left, the “G” channel pixels “light up” whilstimaging the green apple 110. Likewise, the spectral reflectance profile100 of the red apple might nicely mimic the Bayer-pixel spectral profileof the “R” channel. In the lower right, the “R” channel pixels “lightup” when imaging the red apple 120.

FIG. 4 concerns the fact that a scene is effectively never illuminatedwith strictly “white light.” There is always a “structure” to the lightspectral curve—illustrated in very simple fashion in this figure. Inparticular, curve 130 shows the “actual” but largely “unknown” ambientlighting spectral profile of a scene (the apples).

FIG. 5 illustrates a hypothetical “slight green-ish, mainly blue-ish”light source, 140, giving rise to “lighting modified” effective spectralresponse curves B′, 140, G′, 160 and R′ 170.

FIG. 6 shows how the red apple will “look” yellowish, 180—a pretty evencombination of green and red—under the lighting conditions of theprevious figure, all because of the different lighting and nothing to dowith the sensors. The “effective” profiles B′, G′ and R′ all get shapedby the knowable characteristics of the lighting.

FIG. 7 shows that the “standard white” LEDs found in existing cameraphone flashes can be replaced with so-called “Multichip LEDs,” with theEdison Corporation Federal FM series model here depicted (190).

FIG. 8 shows how all of this, to the human eye, looks like apseudo-strobe kind of white light illumination since it is cycling soquickly. In particular, starting with the top, coordinated with frame4*n (n continuously increasing), one of the LED flashes for typically1/30th of a second, 200, for example with a yellow-ish light, yet wellknown spectrally. Below, sensor frame 4*n+1 then coordinates withanother LED flashing for 1/30th of a second, 210, this time with ared-ish looking light, again with well known spectral characteristics.Then below, frame 4*n+2 witnesses a purplish LED flash, 220, tendingmore toward the bluish and green side of the spectrum. Finally, at thebottom, frame 4*n+3 has a mauvish LED flash with its exposure time of1/30th of a second, completing the flash cycle and then incrementing “n”to go back to the top for movies, or stop for a single “image” capture(i.e., n=1 and only 1 for a single image).

FIG. 11 illustrates how some small patch on the red apple, 320,corresponding to a Bayer cell, 330A-D, thus has effectively 12 different“spectral samplings” measured over four frames of image data,corresponding to B0, B1, B2, B3, G0, G1, G2, G3, R0, R1, R2 and R3. TheBayer cell is the same physical cell for all four frames, but withdifferent lighting they have different effective spectral samplingprofiles.

FIG. 12 examines how this sequence of digitized pixel values lets us tryto measure the “unknown” spectral reflection function of the patch ofapple being imaged, including a hypothetical “actual” spectralreflectance function 340 of the patch of apple 320.

FIG. 13 concerns generic linear functional estimation. The left sideshows typical examples of orthogonal discrete functions often used toparameterize (fit) unknown distributions (the apple's true reflectancespectrum 340 in our example). The lower right shows that “smooth”functions can similarly be used, a la Chebyschev Polynomials.

FIG. 14 shows a decent “5-rectangular band” Bayer-tuned Solution Set,with 80 nm, 50 nm, 40 nm, 50 nm and 80 nm bandwidths, respectively.

FIG. 15 shows a 5-band “Orthonormal” set of imaging spectroscopy bands,weighted for direct multiplication with the lighting-modified effectivespectral response curves associated with B0-B3, G0-G3 and R0-R3.

FIG. 16 shows largely empirical coupling value between effectivespectral response G0 and all five chosen bands.

Referring to the left of FIG. 17, the “G0” row of the H matrix iscalculated via simple area multiplications between an empiricallight-source-modified sensor profiles and chosen solution bands (in thecase V-Z). On the right, ‘g’ is the twelve pixel value vector (with theredundant green values averaged); H is the coupling matrix, and F is thesought solution. The G0 row vector is explicitly displayed, while theother 11 rows are implicitly filled-in by multiplying their effectiveresponse curves by the five orthonormal bands, as per FIG. 16. (Thenoted sub-script “p” indicates we are solving for our small applepatch.)

FIG. 22 shows various examples of LED spectral characteristics asplotted on the 1931 CIE spectral diagram.

FIG. 24 illustrates that solution bases functions can be many choicesand not necessarily “orthogonal” or “orthonormal.” Flash-modified pixelsensitivity functions also need not be Bayer/RGB/etc., as well. Heredepicted is how explicit “CIE” solutions can be constructed from“arbitrary” flash-sensor profiles, where multiplication produces rowvalues in our H matrix. Curve 470 shows an arbitrary flash-sensorprofile to be multiplied by any chosen solution functions, heredepicting “classic” 1931 CIE functions. (The subscript “p” againindicates we are solving for our small apple patch.)

FIG. 25 shows that “Direct Chromaticity Capture” becomes a naturalconsequence where (a) sensor profiles, (b) LED profiles, (c) “ambientlight” treatment, and (d) the raw number of independent flashes . . .can all combine to approach near-full-gamut capture, and ever-tighteningerror bars on the capture.

FIG. 26 contemplates that there are many ways to deal with “generallyunknown” but often very typical kinds of ambient light additions to thepure flash, e.g.:

1) add an estimated ambient profile to ALL weight values in the Hmatrix;

2) strobe the flash so quickly, with synchronized strobing of the pixelexposure time, that ambient becomes negligible;

3) EXPLOIT IT! Use a pure ambient capture as part of the framesequencing, giving N-5 in our 4-LED scenario;

4) Use common photographic measuring instrumentation to gauge the colortemperature of ambient, then use this in H matrix correction factors;

5) Use “Flash-Frame Intensity Modulation” to cycle the intensity ofany/all flashes, measuring the digital number modulation of theresulting pixel values against a “known” lumen modulation applied to ascene;

6) Etc. . . . .

FIG. 28 illustrates some of the commercial/consumer applications of thepresent technology, beyond “richest color” photography, e.g., quickchecks on freshness and quality of produce, for both proprietors andconsumers alike (281); building and materials inspection (282); andcounterfeit products “quick checks” (283).

FIG. 31 illustrates how clip-on accessories are a viable short-cut tomarket as the long process of designing and integrating new LEDsdirectly into smart phones. (Depicted is a commercially available opticsupplementation, but making this unit primarily a flash unit with eitherwired or wireless connection to the device is quite viable.)

FIG. 32 illustrates an approach to deal with camera motion and motionphotography (video; effectively motion deblurring in luminance, with theadditional of chrominance “draping”). This involves dynamic linearluminance tracking (keying-in explicitly to time intervals between ⅕thand 1/10th of a second). At 321, “common” luminance-signal correlationcan determine motion between frames, with subsequent re-projection ofindividual frames onto a shared frame—typically the middle frame. At322, the same operation can be done on frames of a video; eachindividual frame can become a reference frame that the other four (inthis example) re-project to.

FIG. 35 posits that the LED units are not on, and a camera merelysamples the ambient light, producing three datum per each cell of aBayer sensor.

FIG. 36 is similar to FIG. 35, but here LED 1 is tweaked on and adistance-squared modified L1 term shows up in the collected samples fromthe Bayer sensor (distance-squared term not explicitly in equations).

FIG. 37 shows that individual LED tweaks can thus be isolated fromambient contributions. Here we see just one LED, number 1, and how weget three “g vector” measurement values that can roll up into matrixequations intending to solve the R coefficients (the unknowns). Forsurface “patches” involving thousands of pixels and allowing several LEDtweak cycles, many otherwise noisy values can nevertheless producesuperb patch spectral patch measurements.

DETAILED DESCRIPTION

FIG. 1 depicts how most modern cameras distinguish red apples from greenapples.

An image of the upper-left-rearside 2012-era iPhone, 40, with cameraaperture on the left, 50, and a small flash unit aperture on the right,60, is shown, along with a simplified Bayer pattern representation ofthe camera's sensor, 70, depicted above the iPhone. With ten or fifteenminutes of discussion with Applicant's early grade school nieces andnephews, it does not take long to explain how the red apple, 20, lightsup the little red-oriented sensors in the camera and the green apple,30, tends to light up the green ones. [See FIG. 3, items 110 and 120 forexplicit intuitive graphics for this only slightly oversimplifiedlesson].

The simplest point is that lighting does matter and any specific‘normal’ camera sensor will have measurably different behavior in itsdigitized signal outputs as a function of the spectral characteristicsof the light used to illuminate some otherwise ‘fixed’ scene. Therelated simple point better made right away rather than later is that,as always, ‘range’ or distance of an object from a flash source is afundamental issue to this technology, just like it is with all flashphotography. Virtually all commercial flash photography has a practicalrange of a few meters at best, maybe 5 or 10 for special types ofphotography. The same types of ranges will apply to this technology,generally considered, and this disclosure will attempt to at least touchupon how ‘spectral fidelity’ will often decrease as a function of range.

Concluding the initial discussion of FIG. 1 then, we find two commonlighting sources for the apples, the sun, 10, and perhaps our smartphone flash unit 60, perhaps individually or perhaps in combination.Obviously there are many other forms of ‘ambient’ lighting beyond thesun as well, and likewise, digital cameras in general have taken thetechnology of ‘the flash unit’ to quite remarkable levels ofsophistication and expense.

FIG. 2 continues the 101-level summary of the technology by presenting ahighly generic but also highly typical plot of the three spectraldetection profiles, 80, of a Bayer-pattern CMOS sensor. The X-axis isthe continuous rainbow blue (400 nanometer wavelength light) to red (700nm). The Y-axis is labeled ‘relative response’ and for this summary canjust mean how strongly light of a very specific wavelength can producesignals in a modern sensor (as manifested by digital values post A/Dconversion). These curves are very familiar to designers of colorcameras, sensor designers, etc. They are also generally familiar to moretechnically inclined photographers. Those familiar with such curvesunderstand that there is great variability and subtlety in how and whythese curves are the way they are, and manufacturers of cameras andsensors spend not inconsiderable time studying and re-designing how suchcurves manifest themselves. This technology adds new, potent variabilityinto the fairly mature and ‘stable’ art of Bayer-pattern filtering inparticular, as will be seen. Concluding the initial discussion of FIG.2, however, it can be noted that by and large these filters have beenand continue to be tuned in such a way that digital cameras can best‘match’ or ‘capture’ natural colors as humans see such colors. Notsurprisingly, these curves mimic what color scientists concisely referto as the CIE color matching functions (and their many subtle variants).

FIG. 3 gets back to our red and green apples and a just-slightlyoversimplified summary of how a camera can measure that a red apple isred and a green one green. We find a new green curve, pointed to bylabel 90, representing an idealized ‘spectral reflectance’ profile of agreen apple, and likewise a red curve, pointed to by label 100,representing the same from a red apple. Color scientists understand thatsuch curves never go to zero for any wavelengths and that thecorrespondence of the spectral shapes to the ‘G’ curve of a Bayerfilter—and the ‘R’ curve—is pretty unlikely. But for this summary,that's just what these particular apples behave, how do you like themapples.

So, for intuition's sake, we can imagine close-ups of our Bayer-patternsensor in a smart phone camera or a digital camera being ‘lit up’ in thegreen pixels, 110, when those pixels correspond to patches of the greenapple, and likewise the red pixels ‘light up,’ 120, for patches of thesensor viewing the red apple. Imaging engineers, etc., all know this‘lighting up’ is simply a nice correlation of innate spectral profile ofan object with the spectral profile of a sensor, hence giving rise tomuch higher digital signal values in the pixel outputs. Indeed, this‘correlation’ is generally accepted to be a multiplication of thequantified spectral light flux of a patch by the also-quantifiedspectral profile of the sensor. Said another way and describedrepeatedly in all books describing color science, this is an integralmultiplication of two spectral curves, one weighted by light flux froman object, the other weighted by spectral quantum efficiency of a pixel,integrated from blue to red. The generally accepted result of such amultiplication are the well known digital number signal outputs frompixels, also taking into account commonly known issues of analog signalto digital count value factors as well. (all too much information for asummary, perhaps; after all . . . we're just showing that green applestend to light up green-filtered pixels and red red!!).

FIG. 4 now introduces a highly idealized ‘ambient’ lighting sourcespectral curve, 130. The main point of this simple diagram is tohighlight that all light sources will have a so-called spectralstructure. Professional photographers learn this in diapers. Astreetwise way to put it is: there ain't no such thing as white light.

The second point to FIG. 4 is that this generally unknown and generallyALWAYS DIFFERENT ambient white-ish illumination will produce slightlydifferent output values to our R, G and B pixels of the Bayer (or other)types of filtered pixels. Again, this is all exceedingly well known toengineers and photographers, with the detailed point of FIG. 4 giving afirst indication of how in this one example, the B pixels will be just atad lower in their resultant digital values IF some object is lit withthis particular type of illumination, RELATIVE TO, the G pixels. Theeffect in this displayed example might be on the order of 20% to 30%less signal showing up in the B pixels than might otherwise show up withpurely ‘white’ signal or equal energy across the spectrum.

FIG. 5 continues the main line of summary from FIG. 4, now presenting anequally idealized but nevertheless instructive case of illumination herecalled ‘slight green-ish mainly blue-ish,’ 140, represented by aperfectly straight line from the upper left to the lower right of thecoordinate background. The deepest point to this figure is that thespectral profile of light can be actively structured! (as every lightingengineer well knows). Depending on the type of lighting source, one'sability to structure illumination spectrally will often be highlyconstrained due to the raw physics of the light source one is using. Forexample, this perfect line from 400 nanometers full-on to 700 nanometersfull-off is theoretically achievable (within, say, 5 to 10% in a 100%scale) using normal tungsten bulbs and some sequence of 5 or 10well-chosen optical filters, but by and large it is not an easy matterto cudgel the spectrum of tungsten to do exactly what you want it to do,it has innate physics thank you very much and that's the palette we aregiven. Later sections will zoom in much more particularly on modern LEDsand the many choices of how to manipulate their ‘raw physics’ into,importantly, economical and practical spectral shapes.

But back to FIG. 5, we now find three new curves depicted labeled B,′150, G,′ 160 and R,′ 170, representing the here-called ‘lightingmodified’ effective spectral response functions of the Bayer pixels. Thephysics of the Bayer pixels will of course not change, but one can now‘know’ how their actual response functions will behave IF one knows thata particular kind of spectral light will be illuminating anobject/scene. The English-phrase way to put this might be: “OK Mr.Apple, I know that in purely white light my Bayer-pattern pixels willread out the signals and colors just like they ought to, but in this newlight where I know the modification of the illumination profile, I alsoknow that my raw pixel output signals will be more like the ‘effective’profiles of 150, 160 and 170. So once again, FIG. 5 uses the commonconvention of putting a prime ′ symbol on the three earlier curves B, Gand R of FIG. 2.”

FIG. 6 further continues this summary line by depicting our red apple,where if we don't tell our Bayer camera that we're using funky light toilluminate the apple, it will dutifully display the apple as yellow on asmart phone screen or some digital camera captured display! The yellowis mainly due to the notion that while the actual reflective spectrum ofthe apple has not changed from curve 100, FIG. 3, its ‘coupling’ ormultiplicative integration with the new spectrally-shaped responsecurves G′ and R′ of FIG. 5 is now more even between the digital responseof the G′ channel and the R′ channel. The R′ channel goes down simplybecause the lighting has much less red in it. And the red apple spectralcurve already had a little bit of coupling into the G channel in thefirst place (even though it is a ‘red’ apple), hence one might imaginethat the resulting yellow will be a ‘dark yellow’ as a nit-pickingmatter. So, the point to FIG. 6, well known to virtually everyprofessional photographer on the planet is: lighting makes a bigdifference to capturing ‘true’ color. FIG. 6 also foreshadows theimportant role of ‘knowing’ what the spectral characteristics of theillumination indeed are.

FIGS. 7 and 8 are probably as general a summary of certain aspects ofthe technology as one can muster. Plop a multiLED flash source in placeof what in 2012 is either a single LED or a ‘white’ dual-LED, thensynchronize its flashing to captured frames from the sensor, most oftenbeing a Bayer-sensor at least for smart phones.

As further disclosure and figures will elucidate, the individualproperties (physics) of each LED within a singularly packaged multi-LEDcan be ‘tuned’ and/or optimized along a variety of design parameters,with ‘cost’ being the perennial Goliath parameter. The result, afterprocessing to be discussed in detail, is that you've turned your smartphone or digital camera into a hyper-spectral imager. More importantlyat a ‘cultural’ level, you've formed the groundwork for explicit ‘truecolor’ or what this disclosure call ‘direct chromaticity capture’imaging. Arcane to many folks but not to color scientists, one now hasthe basis to have a normal Bayer/etc. camera directly produce 1931chromaticity coordinate values, replete with highly testable error barson those values. The physics of the LED choices, perhaps new choices onthe details of the filter curves for the pixels themselves (see FIG. 2),all can combine for an analytic prescription for anticipated error barson such pixel (or small patch of pixels) chromaticity output. One canimmediately appreciate that once new sensors such as the announced SonyRGBW, and once LED spectral characteristics continue their inevitableadvance, then direct chromaticity capture is simply a matter ofengineering decreasing error bars on the values themselves, set againstall the usual variables of distance from an object, glare, ambient lightunknowns (to be discussed at length later), effective temperature of theflashing itself, motion, etc.

To the lay public, this technology will just be another chapter of‘weird stuff’ that can happen when the flash is applied. Many cameraand/or flash manufacturers have been playing games with flash for yearsand decades, so that's nothing new. ‘Everybody knows’ about pre-flashes,flashing flashes, etc. FIG. 8 just summarizes what is going on during agiven ‘flash session’ if you will. Imagining that our CMOS sensor in thefigure likes to expose and frame-out at 30 Hz, we get a glimpse of foursequential flashes, 200, 210, 220 and 230 of a current proto-example ofa multi-LED, 190, FIG. 7. In this case, the four frames will be takenover a 2/15^(th)'s of a second period. By ‘proto-example,’ above, it ismeant that this particular 4-LED device manufactured by Edisoncorporation has not had the physics of it LED spectral emissions tunedor optimized for this particular technology, BUT, even with the innatespectral profiles of their current offerings (none is in figures becauseapplicant has not located any), it is highly likely that even with thisvery specific 2012 model(s) of this device, many of the basic attributesof the technology should work.

FIG. 8 tries to generalize the ‘four flash’ scenario by using the‘4*n+X’ mathematics, where flash 200 gets X=0, 210 X=1, 220 X=2 and 230X=3, thereby accommodating video sequences. A single photo, of course,can just be four flashes and be done. FIG. 8 also continues the somewhatidealized and generic summary line whereby the flash ‘colors’ areobviously different from each other as looked at by a human observer,but subsequent figures/disclosure will explore the spectral aspects ofthese flash sources. It should also be mentioned here that the smartphone itself (and iPhone in particular) is exemplified in the twofigures, but the basic principles are quite applicable to traditionaldigital cameras, where the behind-the-scenes frame/flash synchronizationwill have slightly different physical realizations in digital cameras asopposed to smart phones. The latter are dripping withmulti-functionality and wireless connectivity, and hence are tailor madefor this technology. Digital cameras are more single-purpose typicallyand things such as frame/flash synchronization are already quite‘plumbed’ as they say, but there will be more novelty involved inmulti-frame synchronization surely.

Continuing the summary line, FIG. 9 now blatantly copies FIG. 5 butre-enumerates some of the items to fit the example of FIG. 8. We can nowfruitfully pretend that the particular purplish flash 220 of FIG. 8,derived from the left quadrant LED cell of multi-LED chip 190, FIG. 7,happens to spit out light with the spectral profile 240, our old friendthe idealized straight line from FIG. 5. As later discussion willelucidate, both the physics of LEDs AND the desires of optimizing LEDsfor this technology will probably dictate different results than these,BUT, this straight line still can nicely serve explaining how thetechnology works no matter what spectral profile one winds up with.

So FIG. 9 also presents another important but subtle change over FIG. 5,that is that we have now labeled the resultant effective spectralresponse profiles as B2, 250, G2, 260 and R2, 270. Why? These newnumbers attached to B, G, and R represent the X=2 of FIG. 8, identifyingwhich LED these curves correspond to.

FIG. 10 reiterates this basic point, now imagining that flash LED 200might have a profile that looks like the curve 280 in the figure. Wethen can see the resultant B0 curve, 290, the G0 curve 300 and the R0curve 310. FIGS. 9 and 10 suffice to make these matters clear, such thatone can appreciate that flash units 210 and 230 of FIG. 8 both havetheir unique effective B1, G1, R1 and B3, G3, R3 respectively. All told,we have 12 unique effective response curves, bounding at least for thisexample the number of ‘bands’ we can measure at 12.

FIG. 11 competes with FIGS. 7 and 8 as being a general summary ofcertain aspects of the technology, only this time from the plumbing-sideof the universe. One can imagine that we are in a pretty dark roomtaking a picture of this red apple, maybe 1 meter away from the apple.Our four flashes take 2/15^(th)'s of a second to occur, the CMOS sensorgrabs and stores four Bayer-frames of data. If we then zoom on onespecific ‘Bayer-cell’ of green-red-blue-green, which happens to be‘focused’ onto a tiny patch of the red apple 320 in the figure, we nowcan see the conceptual-yet-palpable explosion of that singular Bayercell into a pseudo-3D array of 12 digital values (16 if we count the G'stwice, but later we shall see that these are averaged in the simplestimplementations). [Later, we will quite explicitly take away thecondition ‘in a dark room’ and discuss the multifaceted and fascinatingworld of bringing normal ambient light back into the scenarios].Rounding out the technical description of FIG. 11, then, we find thelabels 330A, 330B, 330C and 330D applied to the 4 (or 4*n for video)frames captured under the four different LED lighting conditions. Thefigure attempts to be highly explicit that it is the same Bayer celleach time, just different in time and lighting.

FIG. 12 inherently asks the question: now what? So you get these 12independent or 16 dependent numbers, what next?

FIG. 12 for fun fills in some hypothetical and quite realistic digitalnumbers into the 16 splayed “Bayer-cell sub-cells” as one might say. Thequestion is explicitly asked in the figure labeled 350: how does thisarray of 16 8-bit values somehow translate into an estimate for theinnate reflective spectral profile, 340, of the apple patch 320?? Thedepicted curve 340 is explicitly different from the red apple's curve,100, FIG. 3, precisely to illustrate that we don't yet know what it isand we must find some way to estimate it given only the 16 digitalvalues.

A very, very brief side trip into the limitless world of functionalestimation cannot be avoided in this summary line, largely depicted inFIG. 13. This is a laughingly tippy-tip summary of how one can‘parameterize and discretize’ otherwise continuous functions, knowingthat there are trade-offs in the process. The benefit of the process isas simple as it comes: you can estimate functions using a countable setof numbers. The trick then just becomes turning one set of numbers, ouracquired 16 digital values of FIG. 12, into a new set of numbers whichmultiply some chosen set of these so-called bases-functions, hopefullyproducing a function which gets as close as possible to the ‘unknowncurve’ 340, upper right of FIG. 13. The reason applicant felt it wasimperative to take this side trip into an area that many mathematicianstake for granted is that some of the most profound engineeringchallenges of practicing this technology will be contained in thesubtleties of choosing proper bases functions and specifically inmatching innate physics of LEDs and pixel-filtering to such basesfunctions as the 1931 CIE curves. Applicant has not yet performed, yetfull expects to during broader implementations of this technology, verydetailed looks at the performance benefits versus implementation costtrade-offs between, for example, using discrete versus continuous basesfunctions as but one example. The figure shows examples of bothaccordingly, dusting off an old favorite named Chebyshev Polynomials, amathematical gem with an appropriately obscure and evocative name.

FIG. 14, however, evokes the old phrase measure it with a micrometer,mark it with a chalk and chop it with an axe! But this axe is not allthat coarse and indeed, it may for many applications wind up being ahighly useful and practical approach to basic hyper-spectral imaging andthe vast world image processing that entails.

FIG. 14 depicts a ‘custom’ set of 5 basis functions intended to be afirst cut at what might nicely work for both the physics/psychology ofhuman vision as well as the physical practicalities of CMOS/CCD sensorresponse profiles, LED spectra, etc. It is an explicit compromisebetween a purely hyper-spectral system that might posit 5 equal 60nanometer bands from 400 to 700, and one which takes into account thatBayer-profiles already bias raw information content of sensor data intothe ‘photopic’ region of the spectrum, i.e., the region tuned to humanvision. So why not let's tune our ‘simplest’ bases functions (aka‘bands’) to this region as well. We will later discuss the veryimportant bases-function choice of the smooth CIE curves. FIG. 14 thuscontinues the important summary line of the technology, emphasizing howthe basics work and leaving important variants for their own sections.

FIG. 14 presents the newly minted bands V, W, X, Y and Z, how original!V just happens to be violet-ish, Y yellow-ish, but there is no intenthere to sanctify these bands nor tread on the many existing bands ofcolor science and astronomy. The intuitive rationales to thesefunctions, certainly subject to empirical tuning once real Bayer-sensorsand real LEDs are in the picture, include: a) symmetry; b) a nice spreadaround the 1931 CIE chromaticity diagram; c) a coarse ‘couplingbalancing’ between the typical R, G and B curves of a Bayer sensor; andd) a very nice 80/50/40 ratio of the bandwidths, which introduces thenext FIG. 15.

FIG. 15 adjusts these bases functions to become so-called orthonormal, afancy way of just saying the areas under their curves are equal (andequal to ‘1’ if you really want to nit-pick the y-axis scaling). So whatis the deal with these five box functions? The deal is that we are goingto try to estimate object spectral profiles (over each and everyBayer-call of four pixels) using these boxes as our curve-fitters,that's the deal. FIGS. 16 and 17 will take us through the mechanics.

Starting first with FIG. 17, at the highest level we are just going tocreate a very classic ‘linear transformation’ between our 16-valuedacquired vector and our newly minted VWXYZ vector. Give me a 16-valued1-D array of numbers, I'll give you back a 5 valued array, try that withdollars and people, a profit of 11 numbers each transaction, not bad.The traditional form of this transformation, especially when you have asituation where functions behave nice and linear just like spectralprofile multiplication does, is the matrix equation form, depicted asg=Hf.

We will return to FIG. 17 but let's look first to the very elementaloperation required to even talk about a ‘transformation.’ What exactlyis being transformed? FIG. 16 tries to answer this simple question: Anygiven response function (of our 12, with G0 singled out, 300, in thefigure) will ‘linearly couple’ or ‘transform’ or ‘light up’ or ‘chooseyour English word’ into our chosen bases group, here using FIG. 15'sVWXYZ. This is just what it looks like, an area based integration of themultiplication of one curve by the other, sequenced across all fiveVWXYZ bands. To make this a bit more tangible, label 410 is by 5 newentities below the graphic, given the names G0V, G0W, G0X, G0Y and G0Z.These are the so-called coupling coefficients between our chosen basesfunctions and this particular effective response curve. Some crudeestimate numbers are thrown in there both for fun as well as roughlyshowing that they correspond to the areas whereby G0 spreads its energyinto the various buckets, the numbers being typical integrations.

FIG. 17 illustrates our matrix formulation now partially filled out withbona fide numbers. We see twelve numbers in the g vector (420), downfrom 16 because we chose to average our pseudo-dependent G values ineach Bayer-cell. This is the acquired data and it will change each imageto the next. We then can see a shrunken version of FIG. 16, here in FIG.17 now explicitly calculating but one of our 12 rows of the H matrix,430. It is implied that this operation will be done on all twelve rows,using each of the unique individual response functions run through theFIG. 16 washing machine.

Then we find the f vector, 440, now populated with V, W, X, Y and Zsubscripted by a ‘p,’ 450, because we will be performing thistransformation of 12 numbers into 5 numbers for every Bayer cellassociated with all ‘patches’ that make up a full image.

The good news is that this highly explicit matrix equation is notrequired in the implementation of this technology, there are very wellknown ways to create inverse matrices which just vector process12-valued vectors into 5-valued vectors. The steps required in creatingthese inverse matrices can be as involved as the whole functionalestimation world of FIG. 13, replete with ‘regularization’ of poorlyranked matrices and the like, but these topics are not for summaries.The even better news is that the summary section of this disclosure nowconcludes and the remainder of this disclosure will discuss variousnuances and alternatives to realizing this technology, with the800-pound Gorilla being the use of CIE bases functions instead ofhyper-spectral-ish bases functions.

Optimization

FIG. 18 conveys in a single picture that there is all manner offlexibility on the sensor-side of this technology in terms of innatepixel spectral sensitivity profiles. Ever since Bryce Bayer of Kodakdevelop the single-chip color solution, no end of refinement went intofinding better and more cost effective solutions ultimately determiningthe productized forms of the spectral curves. Also depicted in FIG. 18are digital camera spectral curves, 460. One even has four differentspectral curves, all the better, where adding a fourth inherent sensorband merely increases the effective ‘independent’ number of responseprofiles. Sony's rather new ‘RGBW’ sensor lay-out, previously mentioned,is simply heading in directions that this technology can exploit.

FIGS. 19-22 all collectively attempt to convey the very rich ‘designspace’ represented on the LED-side of this technology. Depictedthroughout these figures are various copied diagrams from not onlydifferent manufacturers but different industries as well, with FIG. 21explicitly lifted from a fluorescence microscopy work. FIG. 21 providesanother example of the ability to design spectral shapes aimed atcertain applications, and in particular provides an example fromFlourescence Microscopy. FIG. 21 demonstrates even more flexibility onthe LED spectral-shape side. FIG. 20 displays a fairly typical spectrumof a ‘white’ LED, where this is actually a family of curves showing thatslightly different spectra can be achieved based on a variety ofdesign-scope decisions made on materials, drive electronics and evenphysical temperature if applicable. It is fully anticipated by applicantthat this technology will add another log to the fire well burningalready in the LED industry, a fire which is always pushing for newspectral properties all within generic economic constraints.

FIG. 22 also serves the purpose of a more formal introduction of theheretofore much-touched-upon 1931 CIE chromaticity diagram. A fullintroduction to this rich diagram and its 7 decades of development isradically beyond the scope of this disclosure, and we shall be contenthere to simply say that it remains a bedrock of color science.

This disclosure will discuss primarily using the raw x, y and z 1931color matching functions (FIG. 24) but the reader should understand thatthere are many transformed variants of these functions, includingorthogonalized versions depicted in FIG. 23. All of the subtlevariations have their rationales and areas of strength, so by choosingthe classic 1931 functions this disclosure once again has explicationtrump the black hole of optimization and perfection, an activity bestleft to commercial and proprietary efforts that drive one competitor tohave a winningly-distinguished product over another.

FIG. 23 serves as a form of historic reference on how the design ofBayer-filters for pixels has been related to orthogonal color matchingfunctions. The intuitive trick for Bayer-sensor designers of the pasthas been to ‘generally match up’ the filter-based responses (whichincludes silicon sensitivity functions) to the classic human visioncolor matching functions. With a rough fit thus obtained, a designercould then perform highly sophisticated modeling and testing of how wella given color camera would perform relative to its ability to ‘nail’chromaticity coordinates of objects, AS a function of the innatespectrum of those objects and the lighting conditions—comparing andplotting generally error ovals similar in visual kind (but notsubstance) to the ovals in FIG. 22. In short and perhaps a bit toooversimplified, once a designer finds that physics-based witches' brewof filter goop, they were pretty much stuck with the chromaticity-errorbehavior of the devices. One small objection to Bayer-pattern CMOS overthe years, relative to the wider flexibility inherent in 3-chip colorcameras for example, has been this limitation to goop characteristicsirreverently described. Word on the street in 2012 is that more and moremanufacturers have gotten the goop significantly better where innatecapabilities of the goop matches the functions better and better. In anyevent, the aspects of this technology dictate that getting the goopclose to some of these curves is all well and fine (helpful, yes), butwhen combining this with sequential structured-spectral LED lighting,one now has a whole new dimension to tune in to analytic chromaticitymatching. The upshot of this is that a sensor-LED combination of designprinciples can lead toward an unequivocal engineering pathway towardprecision chromaticity recording, replete withall-possible-object-spectrum variation plots within the CIE chromaticitydiagram itself. In other words, one can model ‘all possiblereflection-spectrum’ objects that have a specific chromaticity, thendirectly see how those objects will be measured—chromaticity-wise—by acamera with Multi-LED flash as per this technology. Error-bars, or errorovals, will still be in full play but adding the LED physics to theparty brings in the steroids.

FIG. 24 then explicitly introduces the classic 1931 x, y and z curvestaught to color scientists in their very first lectures as students. Adeliberately generic LED-sensor combo profile is included, labeled 470.Whatever set of pixel profiles and whatever set of LED profiles producewhatever larger set of combined profiles, they all multiply by thesethree classic curves giving rise to what the figure calls a ‘weight’ inthe matrix, 480, but a dozen different scientists and mathematicianswill give it two dozen different terms. The bottom line is that it is asingle numeric value placed into the H matrix, with this particular CIEmatrix having only 3 columns corresponding to the three classic curves.To the right, then, is the unknown f vector being solved for, labeled490. Same deal as before then: any given ‘patch’ corresponding to aBayer cell, and RGBW cell (maybe even a 9 by 9 cell with 81 differentfilters!) will give rise to this inherent matrix, inverse matrices(vector processing coefficients) will be generated, then out will popdirect CIE color matching coefficients which then . . . voila . . .skipping the mathematical step of turning Xp, Yp and Zp into a‘chromaticity coordinate’ . . . turns into an X, 500, on FIG. 25.

FIG. 25 also wants to compete with FIG. 11, which itself wants tocompete with FIGS. 7 and 8, as being a high level summary of aspects ofthe technology. But FIG. 25 won't win because the 1931 CIE diagram ispretty arcane and contained to the color science community and itsimmediate brethren, AND, hyper-spectral imaging in general goes wellbeyond matters dealing with only human vision. So, we can grant FIG. 25a claim to summarizing one of the most intriguing consequences of thetechnology at least.

FIG. 26 also must play the role that other figures already have playedof being a pointer to rich and varied proprietary activity as opposed toany kind of grand description or summary of such. The subject is how onedeals with ambient light in both a rigorous as well as a practical way.The answer is gazillions.

The figure unabashedly presents a humble text list of five particular‘things’ designers and engineers can do, with anot-possible-to-be-more-explicit suggestion to use common ingenuity andbest engineering practices to develop specific approaches anddistinguish your offerings accordingly. This is not a ‘punt’ of thiswhole topic, it is an act of humility whilst facing design andimplementation issues that hundreds and thousands of very gifted peoplein the past have grappled with, and inevitably as many more will do soin the future. This is where the allusions of religious fervor werepreviously invoked.

So, the list in FIG. 26 starts with a very simple approach whichcertainly should do for most ‘normal consumer’ photography, but surelyeven more sophisticated things will be done even in this application. Towit: design in a little button (or some buried user-choice menu item) asimple switch that has a little sun, a light bulb, and maybe a moon orsomething). Better yet, don't even make the user do anything, justfigure things out from the captured image data itself using many knownimage processing techniques. But, the core approach is to estimate theambient lighting characteristics, especially its general brightnesslevel relative to the flash brightnesses, and just add this estimate tothe H matrix row values outright. This exercise is left to the readerand is well known to those practiced in image processing where ‘ambienteffects’ need to be dealt with one way or another.

Item 2 in FIG. 26 presumes a pretty bright LED source and envisions itspulsing on a fairly short period along with an equally short exposuretime for the pixels. This inherently will bring down the ambient levelsof light simply by reducing the active exposure time OF that ambientlight. For example, 1 millisecond exposures every 1/30^(th) of a secondwill clearly have 33 times less ambient light content than 33millisecond exposures!

Item 3 can be done in combo with other. It is the notion that if youcan't beat ‘em join em.’ By all means take an image with just ambientlight! Simple. You can even use this as an estimator for item 1. You canalso then use it in your matrix equations if you have sufficientconfidence in the ambient light's general spectral profile. If theapplication is ‘decent color photographs,’ a little bit of error is notalways a bad thing, go ask anyone who plays with color in Photoshop.

Item 4 is a kind of cheat but very possible as well. There are so manyphotography gizmos out there, use 'em. Light meters and auto-lightgauges and sunshine sensors (GPS coordinates even) . . . all of thesecan provide useful information to any form of data correction,compensation, etc.

Finally, item 5 is a bit of an odd one but quite workable for the veryserious photographer (or hyper-spectral imaging practitioner). One mightnot know the relatively stable background ‘lumens’ value of the ambientlight, maybe it is say 50 lumens for some given patch of the apple, butone CAN flash that patch with 30 lumens of this flash, then 40, then 50,then 60, knowing that you are pumping in 10 lumen increments, thendifferences on your sensor data should correspond to the ‘knowndifferences’ that you are pumping onto the scene. Patches of objectsshould also respond linearly to these increments as well as absolutes inbrightness, so hey, for you precision measurement types out there thatwant and/or need pretty analytic approaches to fine-scale spectralmeasurements with as much of ambient background removed as possible,this might be your ticket.

Sample Applications

It might turn out that the main application of this technology will bedominated by simply being applied to the many decades of advance incolor imaging, who knows. But this section and a few diagrams tree-topdiscuss some other applications.

FIG. 27 illustrates two of the starker and clear potential medicalapplications of this technology. In both of these cases and many othermedical situations where ‘color cameras’ are used as a core part of thepracticing of some given medical art—hello—hyper-spectral analysis ofpixels will virtually always trump simple human visual color scrutiny interms of raw diagnosis capabilities. Is there hyper-spectral tuneddiagnostic database out there in the world? No, not much yet toapplicants' knowledge, but boy there ought to be. Normal versus abnormalbiological clusters in the colon, esophagus and stomach will allnaturally create more of a ‘signature’ in 4 bands or five bands or more,than they will in human-visual-system tuned RGB. Clearly, Doctors willrely heavily on human color perception as well, but that is not thepoint—fine, keep doing normal color viewing/analysis, but bring a wholenew view to the situation. Doctors have long proven that any new tool ofdiagnosis will be eventually welcomed and put into practice especiallyif the costs keep coming down. FIG. 27 also has dental imaging there forgrins. Applicant would be afraid to use this technology on his own mouthfor fear that I want to go seek professional cleaning far more oftenthan he currently does!

FIG. 28 then attempts to do a modicum of justice to an otherwisebewildering array of potential applications both on the purely 5+bandhyper-spectral imaging side as well as the ‘true color imaging’ side.The beyond obvious application is simple food/produce quick qualitycontrol, both vendor-side and consumer-side. Vendors may freak outthinking that all their customers might some day be inspecting makingtheir fruit purchases with their smart phones rather than the squeeze ofsome grimy fingers, but hang on, maybe that's a good thing? And surelythe cat and mouse game of true quality versus presented quality wouldfind new chapters of sophistication . . . but the point remains, thistechnology has the potential to play here. Likewise inspections,counterfeit ‘suspicions’ if not outright ‘proof,’ all possible. Thefigure is embarrassingly high level in its attempt to summarize theapplications, with surely ten years hence answering the question better.

FIG. 29 then alludes to a slightly more niche world surroundingidentity, printed graphics, packaging, etc. Digital watermarking and‘fingerprinting’ are both well-known methods for identifying objects fora range of applications, and the printing industry has always foundvarious interesting technical gimmicks to spruce up its fare (such ascolor-based stereo printing where colored glasses can reveal 3-D forms,as but one simple example). It is beyond the scope of this technology toexplain why this technology can improve upon these existing arts, but insummary, it can greatly increase effective signal strength in ‘chroma’oriented digital watermarking applications, and the additionalinformation channels and fidelity thereof can greatly increasesignature-characteristics for fingerprinting applications. And gimmickwise, no question, direct graphics can be printed into CMYK objectswhich can't be seen by normal human vision but sure enough, with alittle bit of multi-band distinguishing, come out clear as day in ahyper-spectral image.

FIG. 30 just presents the quick note that any and all ‘traditional flashunits’ of any kind could potentially be ‘upgraded’ to the principles ofthe technology. The need for frame/flash synchronization can be solvedin a variety of ways, including ‘post hoc’ filtering in cases wherethere is no wired or wireless way to do direct synchronization. Bottomline: there is a bunch of legacy equipment out there that with a littlecleverness can be morphed in this technology's direction.

FIG. 31 makes the point that integrating a properly tuned multi-LED intothe actual LED aperture/slot of a smart phone may be practically a fewyears out, and there are highly viable and faster ways to market withthis technology. The depicted smart phone has a not-entirely uncommon‘clip-on’ unit, in this case some extra helper-optics, but there is zeroreason why this can't be a flash unit instead (or in addition to).

FIG. 31A is a block diagram showing selected components of a smartphoneand of such a clip-on accessory. In the phone, a camera control modulesends signals to which the camera sensor responds. Among these signalsis a frame timing control signal, which triggers the sensor to capture aframe of image data, e.g., in a video sequence. The accessory includesan interface portion that receives a version of this frame timing signalfrom the camera. Based on this information concerning the timing offrame capture, a drive circuit in the accessory controls illumination ofselected LEDs in a programmed, synchronized manner.

In one particular implementation, the clip-on accessory plugs into anI/O connector on the phone. For example, the multi-pin connector at thebottom of the Apple iPhone device may be used, or the signal jackthrough which audio signals are transferred between the device andperipherals can be used. In the latter case, the flash accessory may beprogrammed in accordance with audio signals provided to the accessoryunder control of the smartphone processor. The flash unit can interpretthe frequencies and timings of these audio signals as specifying flashesof different LEDs, of different intensities, and of different durations,in successive video frame capture intervals.

In another arrangement, the interface receives the frame timing signalby a wireless connection, such as RFID or Bluetooth or WiFi. In yetanother arrangement, a signal is conveyed from the smartphone to theflash accessory by a wired connection.

Power for the flash unit may be provided from the smartphone (e.g., viaa wired connection), or the unit may have its own battery power source.

While the flash accessory in the depicted arrangements is adapted tophysically engage a portion of the smartphone, so as to removably attachto the smartphone, in other embodiments the flash components can beintegrated into the smartphone.

FIG. 32 quickly treats the important practical issue of motion. Motionof both the camera relative to a scene, but also motion in terms ofvideo. This disclosure has touched upon video mainly as a ‘flashing’ andframe reconstruction issue, this figure looks more at the raw motion ofthe camera frame relative to some external scene. The somewhat maturetechnology of ‘motion compensation’ is explicitly called out in thefigure, where many companies and camera suppliers have already solvedbasic problems of what many call ‘motion blur.’ (This problem is alsoaddressed in applicant's application 61/759,996, and counterpartnon-provisional application Ser. No. 13/842,282 (now U.S. Pat. No.9,136,300), entitled Next Generation Imaging Methods and Systems, whichare hereby incorporated by reference.) Point number one here is: usethem. The figure keys more in on the ideas that different frameexposures correspond to different spectral flashes as a general matter.So, there are then ways to tap into standard motion estimation of theframe relative to a scene, these same approaches can be applied to theluminance element of all frames—their general structure of brightnessvariations, to then ultimately re-associate the pixel patches from oneflash image to another flash image. Image X may need to shift a couplepixels up and over to some master reference frame, and image Y may needto do the opposite. These operations are fairly well known in imageprocessing, mainly dealing with image registration and also‘orthographic alignment,’ with the end result always being improvedresilience to performance degradation due to motion. This area also fitswell into the proprietary methods bucket, where practitioners of thetechnology are highly encouraged to invent improved image registrationmethods.

Light Tweaking

FIG. 33 attempts to describe from a more mathematical angle howarbitrary ambient lighting can be dealt with and mitigated in terms ofits effects on the measurement of surface spectral characteristicsand/or surface color. The mathematical treatment then culminates in amore detailed ‘routine’ that can be applied to the issue ofambient-lighting correction. This routine will be referred to as lighttweaking.

In FIG. 33 we find light sources (representing ‘ambient’ light) withsome arbitrary spectral profile represented as a set of coefficientsmultiplying some orthonormal set of bases functions defined from 400 nmto 700 nm. We see this light source uniformly lighting some flat anduniform surface with a reflectance spectral profile with its own set ofcoefficients using the same orthonormal bases functions. Then we see asingle photodetector measuring the reflected light from the surface,where the spectral response of the detector has yet a third set ofcoefficients describing its properties, again using the same basesfunctions. Those practiced in illumination and light detection arts canappreciate the generalizations in the extreme represented in thisfigure. This is very deliberate so that light tweaking can be clearlydefined and seen instantly by artisans to be viable.

FIG. 34 now introduces a fourth set of spectral coefficients belongingto an LED (or equivalent) second light source also uniformly lightingthe surface. Depicted with this new LED source is the need to be morespecific about distance between a source and an object than with‘ambient.’ For the purposes of measuring ‘relative spectral reflectance’of surfaces, all spectral components of the LED lighting will experiencethe same distance-squared diminution, and hence distance is merely aformal factor which requires noting for a full mathematical treatmentbut which can easily be dealt with in the measurement solution process.We also see three detectors now instead of one, where all three havediffering spectral sensitivity functions and in this particularembodiment, they take on the spectral profiles typical of Bayer-patternimaging detectors or R, G and B. The task to be defined and then solvedis to determine the unknown surface spectral coefficients, 300, giventhe unknown ambient coefficients 310, and the known spectralcoefficients 320 and 330. More particularly, the task will be to makethis measurement even when the light energy from the LED source isdwarfed by the ambient light energy, perhaps up to where the ambientlight is fully ten times brighter than the LED light reaching thesurface, and perhaps even brighter. Ultimate brightness ratios andmeasurement signal to noise properties reduce to classic empiricaltesting, where additional disclosure will show that once thousands andmillions of Bayer pixels are sampling surfaces multiple times persecond, superb surface spectral measurements become possible. The same‘routine’ certainly applies to non-Bayer spectral sensitivity pixels andnon-LED known light source illuminators and much more complicatedambient lighting conditions than that depicted in FIG. 33.

FIG. 35 now expands the number of LED light sources to 4, from just the1 in FIG. 34. Not unsurprisingly each LED has its own spectral radianceprofile characterized by coefficients 340. For this point in thedisclosure's description of the ‘routine,’ FIG. 35 can represent thestate where all LED elements are turned off and hence all L1, L2, L3 andL4 individual spectral coefficients are zero. The next few paragraphsand figures then describe the ‘tweaking’ by this four element LED unit,in contrast to this completely off state of FIG. 35.

FIG. 36 now introduces an individual tweak of light tweaking. LED 1 isturned full on during a sampling exposure of the 3 R, G and B pixels.The sampling duration (exposure time) is identical to that of FIG. 35.FIG. 36 shows that there are now new measured values from the threepixels, 350. For explanatory purposes, these values are only slightlyhigher than those of FIG. 35 so that we can immediately illustrate thatthe LED lighting can be much weaker than ambient lighting and yet as wewill see, good surface spectral measurements can nonetheless be made.Label 360 indicates this by putting the explicit distance fall-off terminto the figure, where we can imagine that the LED contribution might be10% or even less than the ambient contribution.

The light tweaking routine then posits that a 5 frame period cycling ofpulsing the individual LED sources, including a single ‘all off’ state,can illuminate the surface. This cycling would be designed to be inperfect synchrony to the frame rate of a conventional Bayer-patternimaging device (or any monochrome of multi-spectral imaging device aswell). Each frame would isolate some given state of supplemental (toambient) LED illumination, including no supplemental illumination atall. The ensuing mathematical formalism of this cycling can also bedepicted in FIG. 36 if we substitute the appropriate L coefficients intothe equations 350, including zeros for the all-off state of the 5cycles.

FIG. 37 explicitly shows how the unknown ambient lighting spectralcoefficients can quite easily be removed from the aggregate mathematicalequations. In practice, everyone knows cameras move and surfaces move,but by cycling the ‘no illumination’ state along with the LED tweakedstates, a constant sampling of pure-ambient values can take place andinterpolated into the time periods where the tweaked states areoccurring.

Straightforward simultaneous linear equations fall out isolating theunknown surface coefficients in a classic ‘f’ vector, modulated as theyare by the ‘known’ tweak values of the LED coefficients and R, G and B,represented by the classic H matrix, then finally the measured del-R,del-G and del-B values themselves become the classic ‘g’ vector, allrolled up as a g=Hf standard linear algebraic equation. f=inverse Htimes g is the equally classic solution to this equation, with over acentury of prior art methods applicable to properly forming, filteringand shaping such solutions generally with the goal of optimizing signalto noise ratios on the measurement of surface reflectance coefficients.[Note that an additional ‘unknown’ is present—the precise ratio ofoverall ambient light to the LED light; solutions can be formed withthis additional unknown, or, there are methods such as depth-sensingwhich can aid in independently measuring this unknown for applicationswhere this might benefit the overall measurement fidelity; the g=Hfformulation implicitly contains this distance factor and it is only inhighly mobile situations where this additional distance nuance needs tobe worried about as an error component on measurements due to motion].

This section's discussion up through FIG. 37 posits a very simplelighting situation, a simple surface, uniform lighting and only threedetectors whereas modern imaging devices usually have millions of suchRGB detectors. Be this as it may, these simple principles are quiteextensible to small patches of imaging sensors viewing smallpseudo-uniform patches of objects and their surfaces. Ambient lightingconditions can vary quite a bit on ‘normal’ objects and scenes,especially with regards to surface normal (perpendicular directions fromthe surface) relative to where a camera is placed. Applications willrange from extremes where surfaces change their characteristics on a‘per pixel region’ basis, all the way to broad uniformly lit surfacesgiving rise to near-identical measurement conditions across millions ofpixels (think placing a camera up close to a flat color of some graphicprinted paper or package). It is thus entirely expected that theseprinciples described in FIGS. 33-37 will adapt accordingly. Wherecertain levels of ‘region uniformity’ are discovered, thousands andmillions of R, G and B measurements per second can be classicallyaveraged together prior to submittal to the g=Hf solution formalism,culminating into excellent surface spectral measurements even when theLED lighting is 10× fainter, or even fainter, than ambient lighting.

Counterfeit ‘Suspection’

Using the present technology, ink and other manufactured surfaces willbe found to have distinctive ‘spectral signatures’ that can be used toseparate originally printed, authentic articles from counterfeitedarticles. The non-English word ‘Suspection’ is used in the title, thoughthose practiced in the art of counterfeit analysis may substitute‘detection’ as well. There is a subtle yet slightly arcane reasonsuspection is used rather than detection: purists understand thatunequivocal ‘detection’ of counterfeits is an asymptotic goal and never(in practice) an achievable absolute. A milder form of a technical goalis then to strongly suspect something to be counterfeit and then toeither believe that suspicion if its integrity is sufficiently high, or,to subject some suspected counterfeit article to further testing forauthenticity.

A counterfeit suspection device can consist of a clip-on unit similar toFIG. 31. A local or internet library of spectral signatures for variousarticles is stored, and when some given article is ‘scanned’ by thedevice and a spectral signature thus generated, a comparison with storedsignatures is made, with some threshold set separating ‘apparentlyauthentic’ versus ‘suspected as counterfeit.

Specific choices of LED illumination spectral ranges can also be tunedand selected to help discriminate between originals and counterfeits.For example, a specific ink might be chosen which might have very strongreflective properties around 610 nanometers, and then one of the LEDchoices for illumination may similarly have strong illumination at 610nanometers. The strong signal picked up from this concurrence of spectrawould assist in separating originals from counterfeits in the ensuingspectral measurement processes.

Multiple phases of illumination and analysis can be conducted—eachyielding further evidence tending to indicate that a suspect item is oris not a counterfeit.

Spectricity Vectors

FIG. 38 is a diagram illustrating a process of generating spectralimages in response to pulsing a target object with illumination in thepresence of ambient light. The objective of this embodiment is togenerate a form of spectral image data, which we refer to as an Ndimensional “spectricity” vector. This vector has N-dimensions ofspectral components per spatial location coordinate. For example, for animage comprising a 2 dimensional spatial array of pixels, each pixellocation has N-dimensions of spectral components, which we sometimesrefer to as channels. This technology also applies to image sensors thatprovide 3 dimensional arrays of pixel values (horizontal, vertical anddepth dimensions).

The coordinate space of an N-D spectricity vector may also correspond toother domains such as a spatial frequency domain or other transformdomain. Later, we discuss applications that transform (and inversetransform) spectricity images to different domains to derive spectralfeature vectors used in classifiers, object discrimination, and objectidentification applications, including such applications based onsupervised and un-supervised machine learning methodologies. These typesof transformations further generalize the concept of a coordinate spaceof the N-D spectral vector.

Further, some applications employ video capture, which adds a temporalcomponent to the spectricity vector. This temporal component enablesapplications to leverage the variation of a spectral image over time.Just as spectral images may be analyzed in a spatial frequency domain,likewise, spectral video vectors may be analyzed in a temporal frequencydomain and other transform domains that include a temporal component.

The term, “spectricity,” is loosely derived from the concept ofchromaticity, as it represents ratios of a spectral component to atotal. Whereas chromaticity is expressed as two ratios, spectricityextends the number of ratios to N channels, where N is greater than thetypical 2 color space values used to express chromaticity in the fieldof color science.

As described in the methods above, we configure an RGB sensor baseddigital camera to capture images during exposure periods that coincidewith illumination periods of different light sources (in this case,specifically 5 different LED colors in the visible light range). FIG. 38illustrates the processing of captured images in terms of spectralchannels, 100, 102. The processing for one of the channels is detailedin block 100, and this processing is the same for additional channels,as generally reflected by block 102. In this embodiment employing an RGBsensor (in particular, a sensor with a Bayer filter), each raw image iscaptured from a Bayer sensor and provided in the form of digital values(8 bit per spectral component per pixel). The raw image has threechannels corresponding to the R, G, and B components of the sensor. Thelight from an LED light source, as well as the ambient light, couples atleast in part into the R, G, and B components of the sensor.

To help illustrate this point, FIG. 39 depicts a matrix with the colorchannels of the sensor, R, G and B, on the vertical axis, and the LEDlight source colors on the horizontal axis, B, G, R, A, Y (Blue, GreenRed, Amber, and Yellow). In the simplest case of one LED illuminated ata time, the light from that LED is sensed, at least in part, within thethree components of the sensor. For this embodiment, we used LEDsavailable from Marktech Optoelectronics of Latham, N.Y. (“Marktech”).FIGS. 41-42 illustrate spectra measurements of LEDs from Marktech usedin various of our experiments.

In a typical camera device, the image undergoes filtering as well asother possible distortions and corrections (such as gamma correction,white balance automatic gain control, etc.). For five LED light sourcesindividually pulsed, there are 15 channels provided by the sensoroutput, depicted as the cells of the matrix of FIG. 39.

Returning to FIG. 38, the input for each channel is a raw image 104(captured with LED tweak) and a raw ambient image 106 (captured with noLED tweak). Each of these inputs optionally undergoes a process ofreversing image transforms incurred in the image capture process andimage post processing, such as gamma correction as shown in blocks 108and 110. FIG. 38 illustrates the “reverse gamma,” which refers toreversing the gamma correction, as one example of possible reversetransforms applied to undo transforms applied by the camera device orpost processing that occurs prior to application of this method. The boxis depicted in dashed lines, as it is optional depending on whethergamma transform has been applied prior to this point.

After this phase of reversing processing applied by the camera device,the adjusted ambient image is subtracted from the adjusted, LED tweakedimage in block 112 to produce a difference image. In our experiments, weoperate the light sources so that they are about 20% of the ambientlight level, as measured in lumens. Looked at another way, we seek tohave the modulation of light due to LED light sources tweaking theambient light by about 20-30 Digital Numbers (DN) on a scale of 0-255DN, which corresponds to 8 bits per color component per pixel. Theambient light level should be at or below a level such that the lightadded from each LED tweak changes the pixel values by about 20-30 DNwithout saturation. This tweaking of the light around a target objectmodulates the light reflected from the target. The amount of modulationneeded to produce usable spectral images depends on the dynamic range ofthe sensor and ambient light level. Though subtraction is depicted herein FIG. 38, for applications where the ambient light is at or near zero,it is not necessary to capture and subtract the ambient light because ithas negligible impact on the modulation of light from the LEDs.

For example, the sampling instant can be chosen to correspond to a nullin the ambient light luminance—assuming it is predominantly artificiallighting—thereby minimizing the need to counteract ambient light. See,our related U.S. Pat. No. 8,385,971, which is hereby incorporated byreference. In U.S. Pat. No. 8,385,971, there is a passage on ambientlighting, and particularly on exploiting nulls in ambient lighting.

The resulting image (with or without differencing as the case may be) isthen multiplied by a corresponding coupling factor. The coupling factoris a factor corresponding to the channel from the coupling matrix (seeabove discussion about deriving a coupling matrix generally and belowfor another example of its derivation). As noted below, a couplingfactor need not be applied in all applications.

The same processing is applied to other color channels, as generallydepicted by block 102. The N channels of spectral components of theresulting vectors are summed for corresponding spatial/temporalcoordinates in block 118 and then the spectral component value at eachcoordinate is divided by the corresponding sum in block 120 to produce anormalized spectricity vector at each coordinate. Each of the channelscomprises an array of spectral values, each value corresponding to aspectricity ratio measurement for a particular location coordinate,which corresponds to a point or region in space (and/or time for timevarying data capture). To increase signal to noise ratio, for example,neighboring spatial and/or temporal samples may be combined in afiltering operation.

In the example of FIG. 39, there are 15 channels making the dimension ofthe spectral component of a spectricity vector 15 (5 different lighttweaks×3 color components of the RGB Bayer sensor). As a practicalmatter, there is not usable coupling of the light source in eachchannel, and thus, the practical, usable spectral dimension of thespectricity vector is less than 15 (e.g., in some of our experiments,our processes generate spectricity vectors with 8 spectral componentdimensions per location coordinate). Of course, as light sources areincreased and applied in various combinations, it is possible to createmore distinct spectral bands of light tweaks that are then coupled intothe filter of the image sensor.

For the above embodiment, the coupling factors are derived by capturingraw images for each of the light source tweaks reflected from a whitetest sheet. The resulting images provide a measure of the coupling ofeach light source tweak into the filter corresponding to each colorcomponent of the sensor. From this measurement, a coupling factor isderived. While this coupling factor is not required in all applications,it is useful for applications to calibrate data from different lightsource—sensor pairs. The calibration process is: determine couplingmatrix for light source—sensor pair, and apply coupling matrix for thatpair to produce spectral images, and repeat this process for differentlight source sensor pairs used to collect spectral images. Forapplications where calibration of different devices is not an issue, thespectricity vector can be used without applying a coupling vector.However, even in such applications, it is useful to be able to ascertainthe coupling so that it can be taken into account in subsequent use ofthe spectral content, to remove un-desired bias that the coupling mayintroduce in the spectral images.

FIG. 40 illustrates a method for determining coupling factors. Takingthe matrix of FIG. 39 as an example of spectral channels, we illustratethe process as follows. Each cell in the matrix of FIG. 39 correspondsto a channel in which the light emitted by an LED during an illuminationperiod and reflected from a test patch is captured through one of thecolor components of the camera sensor. One can think of the channel 130depicted in the process of FIG. 40 as the output of block 112 of FIG.39, with similar options and variations as discussed above (e.g.,reversal of transforms, differencing to subtract ambient, etc.). Foreach of these channels (130), the process of computing the couplingfactors sums the pixel values over the patch area 132. Next, the processnormalizes the coupling values by dividing by the maximum sum that isdetermined as the maximum from the sums of patches measured for all ofthe channels 143. The coupling factors are computed by inverting thecoupling values 136. This provides a factor for each channel that isapplied by multiplying it with a corresponding pixel values for thatchannel (e.g., as shown in blocks 114 and 116 of FIG. 38).

As illustrated further in code listing examples filed with thisapplication, calculation of the coupling factors for a coupling matrixmay also entail a process of removing measurements that fall below athreshold, as a form of filtering out un-wanted contribution from noisesources.

Cross Reference to MatLab Code Examples

As noted above, this application includes a computer program listingappendix including the following Matlab computer program files:Spectricityv11_multiday_set2-code appendix.txt, SpectraImg-codeappendix.txt and spectraId-code appendix.txt, configParser-codeappendix.txt, all incorporated into this specification. The file,Spectricityv11_multiday_set2-code appendix.txt, includes Matlab codelisting instructions for computing spectricity vectors, calledspectricity images, and for colorimetric mapping (see below). The filesnamed, SpectraImg-code_appendix.txt and spectraId-code_appendix.txt,configParser-code_appendix.txt, are related as follows: SpectraId-codeappendix includes a main Matlab script, configParser-code appendix isused to run this main script, and SpectraImg-code appendix includesinstructions for computing colorimetric mapping (referred to as truecolor, see CalcTrueColor function), for computing a coupling matrix andspectricity vectors, etc.

Colorimetric and Other Mappings Derived from Spectral Images

An RGB camera effectively attempts to estimate the chromaticitycoordinates of all objects in a scene. This estimate is notoriouslynoisy and error prone due to many reasons, with a significant reasonbeing ‘lighting.’ This observation is illustrated in FIG. 43. FIG. 43illustrates chromaticity errors caused by an RGB camera. The black andorange stars represent how the chromaticity value in color spaceprovided by an RGB camera is different than the correct value (Redstar). Due to errors within the camera, the actual value at the red staris misinterpreted by the camera to be the chromaticity value at theblack star, even without lighting related errors. Additional errors inchromaticity measurement occur due to the type of light, as representedby the chromaticity value under natural sun lighting (orange star nearsun graphic) vs. the chromaticity value under artificial lighting(orange star near the light bulb graphic).

The chromaticity is a 2 dimensional vector (e.g., in CIE coordinates,CIE_x and CIE_y), whereas the above described spectral ratios providemore useful N dimensional spectral ratio values for object surfaces,more stable relative to lighting conditions and with greater than 2dimensions of ‘useable signal.’

To provide a more reliable and accurate measurement of chromaticity, theN dimensional vector of spectral ratios obtained by the above methodsare mapped into 2 dimensional chromaticity space. More generally, thismapping can be adapted to map spectral vectors into a variety of colorspace standards, such as CIE and others.

This colorimetric mapping is achieved by capturing standard color charttest patterns (e.g., Gretag-MacBeth or ColorChecker color renditionchart, etc.) with the above spectricity vector methods. A color mappingtransform matrix is then derived to map the N-D vector into 2Dchromaticity coordinates. Color images generated from this methodprovide more accurate colorimetric measurements using less reliableimages captured through a Bayer sensor.

Once measured this way, the color temperature of the light falling ontoa scene can be subsequently measured in the process. The methods of thisdisclosure enable the spectral composition of the lighting, includingthe ambient lighting to be measured, corrected and mapped into a colorspace domain in which the color temperature is computed.

As illustrated throughout this document, there are many applications ofthese techniques. The use of reasonably precise LED light tweakingwithout much regard to ambient conditions is a powerful feature. Thiscan be leveraged significantly with machine vision techniques and someof our well-used correlation techniques. Machine vision can be used tostitch together (and optionally construct a 3D model from) manyambient+LED combined images taken by viewing a scene for severalseconds. Exposure time and/or illumination period of LED (time a LED isturned on) for each frame can be optionally varied in some pseudorandommanner. After tying object pixels together through the many images withmachine vision methods, the various LED reflectance values for eachobject point can be estimated with knowledge of the various exposureinformation. We elaborate on several more enhancement and applicationsbelow.

Errors in Spectricity Measurements and Various Approaches to MitigatingThose Errors

Above, we described principles involved in measuring the spectral ratiosand/or LED-pixel sensitivity ratios (the latter involving thewavelength-distribution mixing of LED spectra with the sensitivityprofile of a pixel) of surfaces. This section provides further detailson common error sources that often arise in actually implementing theseprinciples, along with explications of approaches that can be used toestimate these error sources and mitigate them. The next two sectionslay some groundwork for these topics.

Object Surface Changes vs. Measurement Errors

The technical goal of spectricity measurement is to accurately measurethe innate surface reflectance properties of some patch of a surface. Ameasurement results in a spectricity coordinate for a patch, also calleda spectricity vector for that surface. Ideally, this vector iscompletely determined by the optical properties of the surface inquestion. At some level, all surfaces will have changes in their opticalreflectance properties over characteristic time periods: a light greypatina developing on stainless steel cutlery over a few years versus aquick weeks-scale rusty reddening of an iron chain left out in the rain;quicker still, the hours-scale bruising of a fruit, and theseconds-scale blushing of a cheek. These intrinsic optical changes tosurfaces are just what we are looking to measure; they are not errorsources of course.

Errors can be broadly defined as any changes in a measured spectricityvector value for some specific surface which itself has no changes inits optical properties. There are numerous sources of errors within thisbroad definition and these sections will concentrate on some of thelarge error sources along with their mitigations. Three specific errorsources and their mitigations will be described: 1) Field AngleNon-uniformity; 2) Surface innate-reflectivity non-linearity; and 3)Surface Normal effects due to under-sampled Bi-Reflectance DistributionFunctions (BRDF) (to be explained in its own section).

Light Reflectance and a Split Between Specular and Diffuse Reflection;the Bidirectional Reflectance Distribution Function

FIGS. 44-45 below provide further context for the ensuing disclosure.FIG. 44 depicts that an incident beam of light (e.g., from a focusedLED) generally gives rise to BOTH these two types of reflection—1)specular, as if the surface was a mirror, and 2) diffuse, as for a toughsurfaces; different surfaces have different ratios of how much lightreflects into these two modes.

As depicted in FIG. 45, extremely precise applications can be even morespecific in describing how much light from one angle, Wi, gets reflectedinto another reflectance angle Wr. This is the somewhat arcane 4dimensional ‘Bidirectional Reflectance Distribution Function’. Insmartphone implementations, with the lens and the LED source beingnearly co-located, Wi and Wr are almost identical. LEDs and cameras donot necessarily need to be co-located, and hence the fuller BRDF viewcan be important to understanding spectricity error sources.

FIGS. 44 and 45 briefly summarize some salient properties of reflectedlight. In each figure, an idealized illuminator comes from some specific‘ray angle’, giving rise to scattering of light into all angles. FIG. 45depicts a light detector which presumably can vary across all angles Wr.The full BRDF becomes a four dimensional function once the hypotheticallight source direction onto the surface also varies across all angles,with each incident light angle (Wi represented by two variables)reflecting light into all angles (Wr represented by two more variables).Indeed, as pertinent to this disclosure, it becomes a 5 dimensionalfunction once wavelength-specific measurements are considered. Thisspectral aspect can be approximated to be nearly uniform acrosswavelengths but for many spectral imaging applications, this might be apoor assumption and further errors in spectricity measurements willresult.

One main point for this disclosure is that many configurations of thistechnology posit a single camera and a generally-singular, compact LEDlighting unit. In mathematical terms, such an arrangement positslighting a given surface from one specific angle Wi, then viewing thatsurface from a typically co-located or equal angle Wr to Wi. Theresultant measurement from that specific point in the 4 dimensional BRDFthen becomes a proxy for all values in the BRDF. To the extent thissingular measurement cannot properly describe the aggregate reflectanceproperties of a surface as represented by the full BRDF, then suchdiscrepancies must be chalked up as error. This disclosure refers tothis error source as ‘undersampling the full BRDF’. There is yet a fifthdimension to the BRDF once one considers monochromatic light as theincident light, as already noted. To the extent the BRDF is rathersimilar from one wavelength to another, or not, this will be a factor inthe extent of error introduced by this particular source of error withregards to spectricity characteristics of surfaces.

At an academic level, the undersampled BRDF source of error can appearto be rather egregious, and indeed, for very high end applications suchas chemically designing inks and paints for example, these potentialerrors can be quite important. But fortunately for many otherapplications such as mobile device identification of common objects andsurfaces, the specular versus diffuse error-source situation depicted inFIG. 44 is more practical concern than the errors due to undersampledBRDFs.

Field Angle Non-Uniformity Error and Mitigation

One of the principles of this disclosure posits that one given LED willdifferentially (by adding to ambient) illuminate surfaces in a scene,followed by another LED, then the next, etc. An implicit but here nowexplicit idea behind this is that the generic ratios of illuminating‘differential light tweaks’ remain relatively constant with bothdistance of a surface from the camera/LED combination, as well as fromthe center of a scene out to the edges of a scene (i.e., the surfacesilluminated position in a scene relative to the center of the scene).For all physical realizations of this technology, this perfect constancyof LED illuminant ratios is not possible once one considers thesituation at the few percent level (percent differences in ratios forexample). The consequence of this deviation from strictly uniformlighting is that the raw measurements of spectricity vectors onotherwise identical surfaces will change both with distance and withwhat common practice calls ‘field of view angle’. In general, the lattereffect of changes due to field of view is more pronounced than thechanges as a function of distance, but this is ultimately a function ofdetails of how the optics of the illuminating LEDs are designed (e.g.,broadly diffuse lighting versus ‘focused spotlight’, as but oneexample). Distance changes may become as important as field of viewangle changes, in other words, it will be application and lightingdesign dependent.

FIGS. 46, 47 and 48 provide visible examples of the field anglenon-uniformities. Figures after these abstract the notions and lead to avariety of solutions to mitigating errors introduced by theseunavoidable physical effects. Ordinary sheets of paper are used forseveral reasons not least of which is that they could quickly prove afew points. There is in fact edges and details in the images, but theoverall field angle non-uniformities can still be illustrated as well.

FIG. 46 depicts green LED differential lighting of some white papersheets. This lighting is in addition to a modest level of ‘normal’ambient diffuse lighting. Hence the LED lighting is differentiallymodulating the pseudo-uniform scene. In practice, a uniform whitesurface, commercially made white targets, or simply ‘good enough for anygiven application’ white surfaces, can be used as a scene.

One can visibly see in FIG. 46 that a normal kind of brightening in themiddle of the scene is surrounded by an equally normal dimming as onemoves out from the center.

FIG. 47 depicts the same scene as FIG. 46, but now differentially lit bya blue LED one frame in a video sequence later, where the pulsing of theLEDs are coordinated with the framing of a camera—a Bayer-pixel colorcamera in this case. The LED part used in both this figure and the lasthas seven 200 micron by 200 micron active LED ‘chips’ tuned to differentmodestly narrow bands in the spectrum. The placement of the LEDs are ina small ring of approximately 3 millimeter breadth, where physicalwires/leads are present in the direction of illumination, i.e., thewires subtly affect the far field illumination pattern.

Comparing FIGS. 46 and 47 is of course not easy without furtherinstrumentation to assist, but suffice it to say that the detailedilluminant profile of the green LED, referenced say to its peakillumination point in the scene, is definitely different from the blueilluminant profile if one considers those profiles at the ˜1 to 10%difference range. Likewise, the same is true for the other 5 LEDs in theparticular 7-element part used in this example. One can appreciate thateven the flatness of the 200 micron active elements will produce an everso slight shift (perhaps 5 to 10 degrees) in the precise peak locationof its light energy in the far field.

The same process used to obtain the images of FIGS. 46 and 47 is used toobtain images for three other LEDs, which were used to illuminate thesesheets of paper.

FIG. 48 provides an ‘iso-spectricity overlay’ image of the processedscene.

More specifically, FIG. 48 depicts an iso-spectricity overlay image ofthe white sheets of paper, each separately illuminated by the 5 LEDs.The ambient lit scene is the backdrop, whilst a 15 dimensional vectorvalue of a random point in the center of the scene is used as a‘reference value’ and all the other measured spectricity vectors in thescene are compared to it, with simple Euclidean distance used as amodulator on the ‘red’ that gets overlaid into the image.

Those practiced in the arts of lighting, image measurements,chromaticity measurements and even those schooled in higher dimensionalvector mathematics can all appreciate that there is a great deal morethat could be explained here; later sections will indeed explore more on‘iso-spectricity’ visualization for example. BUT, the point for thissection is that FIG. 48 clearly and intuitively shows that for evennormal white sheets of paper which ‘should’ have relatively uniformspectricity signature vectors, raw measurements of those vectorsappreciably change as a function of field angle.

The magnitude of these changes are somewhat exaggerated in FIG. 48 inthat the iso-spectricity thresholds that needed to be set can zoom in onthe ‘couple to few digital numbers’ range, right close to the noisefloors of most normal cameras, and hence even a few percent change inuniformity between one LED and another can produce the obvious effectsillustrated in FIG. 48.

So, knowing that these non-uniformities can produce tangible errors inspectricity vector measurements, we proceed to a discussion of what canbe done about them.

FIG. 49 contains a summary of largely what FIGS. 46-48 have shownexperimentally, followed by further figures and explanations of boththeoretical procedures and actual calibration procedures that can beperformed to mitigate these errors.

FIG. 49 is intended to illustrate the following: Finely conductedexperimental procedures on calibrated ‘white photographic panels’ showthat as one performs the operations to obtain spectricity values on sucha white panel, one will produce a curved/warped 2 dimensional sheet ofspectricity values in N-dimensional space, where N=15 in the previousfigures. The N-D Spectral Signature of the image of a ‘white sheet’should all be the same, but even the most calibrated camera with themost calibrated lighting will produce a resultant ‘sheet’ in N-DSpectricity Vector Space (or its ‘Signature’). Even the most carefullydesigned uniform illumination system will still have measurablenon-uniformities if one pushes hard enough to find them. Thesenon-uniformities are depicted in the distortion of the sheet in FIG. 49.

FIG. 49 is making an implicit point: For a relatively fixed physicalarrangement between a camera and some given multi-LED illumination unit,a relatively stable calibration of the non-uniformities can be measuredand ultimately ‘displayed’ or at least conceived of as a 2 dimensionalwarped plane in an N dimensional space. There is little need to actuallytry to visualize such a sheet, but there are in fact ways to try to dothis visualization that will be touched upon in subsequent sections.

Practically speaking there are both theoretical ways of approximatingthe numeric behaviors of these 2D warped sheets (through knowledge ofthe design of the LEDs, its illuminating patterns, and the like), butmore importantly empirical ways to measure these sheets in ways that arepragmatically stable for weeks, months and perhaps the lifetimes of anygiven physical arrangement, smartphone based or otherwise. One canimagine making and storing actual measurements of the calibrated whitepanels at all the cross-points in the depicted sheet above. One can alsothen ‘curve fit’ 2 dimensional sheets within the N-dimensional space tothe measured data, thus smoothing out high frequency errors in themeasurement of these sheets and arriving at a mathematical descriptionof the specific sheet for a specific camera/LED unit combination.

FIG. 50 provides an illustration that explains a process of fieldcorrection. After a camera/LED's warped sheet has been measured, reducedand stored, then all subsequent spectricity measurements using thatcamera/LED apply correction vectors as a function of field angle, usingan arbitrary reference point such as the ‘white’ spectricity vectorvalue found at the center of a scene. All other field angles getcorrected to this center point.

FIG. 50 also helps illustrate how ‘stored sheets’ become a kind oflook-up-table that become spectricity vector correction values to allsubsequent measurements made by the camera LED combination. Thosepracticed in the art of light measurement fully understand that therewill still be finer-scale error sources involved with these kinds ofcorrection operations, and specifically that corrections applied to‘effectively white’ surfaces may differ measurably from surfaces thathave more complicated spectral structure, but the point of this sectionis that the gross behavior of field angle errors can be mitigated if notentirely removed. A rule of thumb design target for common commercialapplications would be to mitigate ‘spectricity blurring’ as a functionof field angle by up to an order of magnitude, if possible. Intuitively,as well as empirically, one can appreciate that if these procedures arefollowed and subsequently a ‘red sheet’ or a ‘green sheet’ is measuredby a so-calibrated camera—LED pairing set-up, the resultant ‘spreads’ ofthe spectricity vector values of those sheets should be nearly an orderof magnitude tighter in comparing raw vector value spreads to calibratedspreads. At the end of the day, ‘error mitigation’ largely boils down tosuch measurement and verification considerations. As shown in FIG. 50,the signature at a point near the center of the image is chosen as thecorrect signature. In this process of pixel by pixel field correction,all other pixels in the image get a correction vector applied to themdue to the field non-uniformity (the blue vector applied to the redpixel corrects its value).

FIG. 51 next delves into the slightly counter-intuitive but all tooprevalent situation where the level of reflected illumination from asurface, as well as the detailed linearity behavior of normal cameras,can produce additional errors in spectricity measurements which alsothankfully can be mitigated.

FIG. 51 depicts spectricity errors caused by gross reflectance values(i.e. lightness-darkness of surfaces).

FIG. 51 explains that if we now replace the bright white panel with onewhich is a mid-level and still calibrated ‘grey’, virtually everyreasonably precise (modest laboratory/dark-room setting) will exhibitmeasurable shifts in spectricity vector values between the sheetmeasured with the white panel and the ‘new grey sheet’ measured on thegrey panel. A similar effect happens when a ‘grey sheet’, with identicalspectrum to a ‘white sheet’, has its spectral signature measured: itssheet shifts around in ‘signature space’. This is also due toever-so-slight non-linearities even in high end ‘gamma=1’ cameras. Thedegree of this effect is rather exaggerated in FIG. 51, but the point ismade. Indeed, it is a testament to the higher fidelity measurementcapabilities of even normal smartphones that these slight shifts caneven be measured at all.

There are a variety of causes of such shifting, as with the white panelalready described. A leading cause is simply is that the silicon sensorsinside every camera always have some level of non-linearity if only atthe physics level of the pixels (which is a very small non-linearityindeed). For many applications the degree of reflectance level error maybe too small to care about, for others it may be necessary ofmeasurement and mitigation.

FIG. 52 depicts reflectance-level spectricity vector correction.Inherent luminance of the reflected surface point also becomes a factorin calculating then applying the signature correction vector for allpixels (corrected to the ‘full white’ center pixel, an arbitrary globalstandard point). This correction process uses a similar process as theone for FIG. 50. As with FIG. 50, additional ‘grey level sheets’ (oftenjust two or three can nicely sample the range from black to white) aremeasured, stored, then a given measured spectricity value. Thesevolumetric correction maps are created by literally putting white sheetsand calibrated ‘grey sheets’ directly into the stage of the camera/LEDset-up and collecting the appropriate data. The correction processaccesses those sheets and generates an appropriate correction vector.

Both the raw ambient luminance channel of a scene, as well as the totalreflected LED signal level as determined after an LED cycle has beencaptured, can be used to provide a measurement of the reflectance levelof a given surface in any given part of a scene.

One final important point in this section on mitigation of errors due tofield angles and innate surface luminosity is that the vast variety ofcommercial cameras, both color and black and white, all one way oranother have been designed with the human visual system (HVS) in mindand they all have their own brand of camera specific image processing.This is a category of image processing that is programmed into moderncameras to tune camera performance. Yet this image processing (e.g.,camera specific image correction designed with HVS in mind) are allpotential sources of error in spectricity measurements if they are noteither turned off or otherwise factored in to the measurement chain ofspectricity vectors. Auto-gain, white balancing, nearest neighbor Bayerprocessing, gamma, are a few of the examples of such processing. Somebut not all of the measurable effects illustrated in FIGS. 46-52 cantrace their roots to these internal camera processing functions. Gammain particular is an important issue and other sections of thisdisclosure discuss its ramifications and corrections, as one example.

The baseline rule is: If a given reference surface with stable physicalproperties nevertheless has differing measured spectricity vectors as afunction of some discernible environmental condition, the cause, thenthat cause becomes a candidate to objective measurement of its inducedspectricity vector changes and then subsequent mitigation. This genericbaseline rule is clearly applicable to all empirical measurementarrangements of course, but its applicability to this disclosure is madeexplicit.

Specular Versus Diffuse Reflection Ratios

Recalling FIG. 45, the specular versus the diffuse reflectioncharacteristics of various surfaces are rather important to understandand wrap into the baseline principles of this disclosure. Those of ushaving the privilege of normal vision have an intuitive connection tothese differences in reflective properties, largely summarized by thedegree of shiny versus matte of surfaces and everything in between.

Fundamental physics teaches us that the spectral content of diffuseversus specular reflection from most if not all surfaces will differfrom each other if not largely then at least at the finest spectraldiscrimination scales. A driving reason for these differences is thatspecular reflection tends to be more involved with the physics ofair-matter surface phenomena, while diffuse reflection tends to dealmore with surface penetration and subsequent interaction (oftenabsorption) with near-surface matter. At a crude high level, specularreflection tends to exhibit more pan-spectral uniformity than the morespectrally-selective properties of normal matter.

This all matters to this disclosure for a classic double-edged swordpair of reasons:

1) A given physically stable surface can have significantly differentspectricity vector measurements depending on whether or not thecamera-LED combination is ‘normal’ to a surface versus at some angle;

and

2) These differences in spectricity can be exploited in a variety ofways, most notably in that they a) provide additional information onsurface topologies and b) 2 dimensionally sample overall 3 dimensionalobject properties as projected onto the camera, both of which cangreatly assist in object recognition among other things.

So the pseudo-negative side of that double edged sword, the practitionercan expect measured spectricity vectors of surfaces to vary as afunction of the surface-normal vector relative to the cameracenter-axis. This will be the case specifically for set-ups where theLED unit is co-located with the camera within a centimeter or twolaterally to a camera lens, or even LEDs circled around a lens.

But before diving in further, FIG. 53 attempts to further ground theseconcepts:

FIG. 53 is a normal color photograph of a scene with both diffuseambient lighting as well as one distinct thermal light source castingshadows. The intuitive notion of specular reflection can clearly be seenas a white-ish glint on the pear as well as on the nectarine.

FIG. 53 grounds us in our intuitive notions of specular versus diffusereflection. Images of billiard balls work nicely in this regard as well.The image of FIG. 53 was taken with a normal Bayer-type color camera.The existence of shadows brings out the further subtlety that some levelof diffuse reflection can derive form the thermal source, while otherreflections in the shadows are mainly from ambient diffuse reflection.

FIG. 54 is an image of the same scene and camera set-up as FIG. 53. Nowthe ambient light has been significantly dimmed and is largelydetermined by a distant thermal light source, itself reflecting off of abroad ceiling. This ‘ambient lit scene’ will now be studied and used forexplaining further inventive aspects of our technology.

FIG. 54 now sets the stage for not just discussing the specular versusdiffuse reflection issue, but also for further practical details onspectricity measurements and their resulting properties.

The ambient lighting evident in FIG. 54 gives rise to pixel values inthe upper right white panel in the 100 to 130 digital number range on a255 8-bit scale. Subsequent additional illumination of this scene by 5different band LEDs gave rise to an increase in ‘average’ digitalnumbers of pixels by roughly 20 to 30 digital numbers all depending onwavelengths and the R's, G's and B's that preferentially responded tothe various LEDs and color patches. At a crude high level, the‘differential tweaks’ from the LEDs, obtained by subtracting the ambientframe from the individually lit frame, was on the order of 20% to 25% ofambient. A long term goal is to see if these differential tweak levelscan approach 10% of ambient, but 20% to 25% is a good place to start.

FIG. 55 is an image obtained from the same ambient lit scene as FIG. 54but now with the ‘differential tweak’ of the blue LED turned on. Themeasurement set-up here had the scene at about 20 inches from a normalBayer camera, while the LED unit was displaced by about three inches.Smartphone integration or ‘rings of LEDs around lenses’ will not havenearly this level of separation, but for these studies and forexplaining the principles in our disclosure, this separation can proveuseful, starting with noting ‘the shadow’ in the light green panel tothe lower left of the pear: the pixel levels in the shadow next to thepixel levels in the ‘lit’ side of this green panel clearly illustratethe ˜20 to 25% level of differential tweaking of the scene.

FIG. 55 has four other counterpart images where ‘red’, ‘amber’, ‘green’and ‘yellow’ LEDs were individually lit. Just for further illustration,FIG. 56 shows the green tweaked image.

The Green LED tweaked image of FIG. 56, taken less than one second laterthan the ambient image of FIG. 54 and the blue-tweak image of FIG. 55.The timing is not critical for these set pieces but the broader idearemains that the LED tweaks are either frame synchronized with a camera,or, at least timed such that individual LED tweaked data is derived fromthe raw imagery itself (see demux discussion herein), as is often thecase with rolling shutter image data where part of a frame has good‘full tweak’ data and other parts may have none (as a function of scanlines typically).

Getting back to the theme of this section, specular and diffusereflection, examination of FIGS. 55-56 shows that the subjectivelocation of the ‘specular shininess’ on both the pear and nectarine haveboth shifted from their locations evident in FIG. 53. Also, at anintuitive level, one can see in both FIGS. 55-56 that this new locationis much closer to the ‘surface normal’ of these two fruits, relative tothe camera main axis. Thus, the specular reflection is closer to wherewe expect it to be.

One mitigating factor in the negative-side view of specular versusdiffuse reflection begins to reveal itself in FIGS. 55-56. That is, allthings considered, the specular shiny spots are not too big at leastrelative to the full sizes of the pear and the nectarine in theseexamples. These types of effects, as described for similar effects, aredetected and mitigated, as appropriate, to achieve the broader goals ofmost applications: identification and evaluation of objects.

The total sum of only the differential LED light tweaks is now presentedin FIG. 57. Specifically, FIG. 57 depicts the sum total of the increasesin pixel values measured for each of the 5 LED-ambient images (their rawdigital number increases across R, G and B values), displayed as a blackand white image.

FIG. 57 is interesting in many ways but not least for its additionalevidence of the differences between specular and diffuse reflectioneffects. If we take the reasonable assumption that most of the cameraprocessing non-linearities have been accounted for in the differencingoperation producing the so-called ‘pure’ LED-tweak images (basicallyFIG. 55 minus FIG. 54, FIG. 56 minus FIG. 54, and likewise with thethree other LEDs), then FIG. 57 is a good representation of ‘just theadded light from the LEDs’, all put on top of each other. This was ourflashlight made up of five individual LED flashes.

Given the rather dim condition of the outer-field patches and theborders, it can be appreciated that even in 20% to 25% LED tweak toambient conditions, the resultant LED tweak data is pretty low except inthose areas closer to the LED flash/camera unit, and obviously of awhiter nature. Thus, one aspect of this disclosure is here illuminated,that being that weaker signals can be more of the norm than theexception as various practical applications will not be tolerant of‘battery draining and eye-blinding’ LED flashing.

An additional explanatory benefit of FIG. 57 is that this frame,augmented by the value ‘1’ in any pixel location that might happen tocome out as 0 due to normal noise, is precisely the ‘sum’ frame that allother differential frames will be divided by in order to obtain rawspectricity values for individual patches in the scene.

Concluding this section on specular versus diffuse reflection at leastin terms of the negative-side of ‘error sources’, we finish by notingthat methods can be designed to measure/identify patches within imagescaptured by these methods which are more prone to specular reflectionand which are oppositely prone to diffuse reflection. In particular,ratios between the two are estimated on a scene-patch by scene-patchbasis. Then furthermore, the resultant measured spectricity vectors forthose given patches are thus ‘labeled’ by their S to D type reflectionpropensity. Object-type specific characterization can then be performedbased on how spectral content changes as a function of moving fromS-type reflection to D-type reflection.

More on Under-Sampled BRDFs, Potential Spectricity Vector Errors

Returning again to FIG. 45 and related discussion, at the heart of thedefinition of the BRDF is the notion of the surface normal and variousorientations relative to light source and observer. This in turnemphasizes 3 dimensional space and that these entities must be describedin 3 dimensional space.

The negative ‘error inducing’ aspect of under-sampled BRDFs has alreadybeen introduced. Reviewing FIG. 45, to the extent a spectricity vectoris measured for some specific lighting and viewing angle, the assumptionis made that the measured value is reasonably correlated to all other—atleast diffuse—locations in the four dimensional BRDF. Again, from someamount of experience of applicants, this is a decent assumption for manysurfaces, bearing in mind the previous discussion on how specularreflections might creep into any given situation. When large aggregatesof patches are sampled presumably belonging to an integral objects,presumably having a reasonably similar spectral profile on most exposedsurfaces, then a de facto larger sampling of a population of relatedBRDFs is happening by simply forming ‘an image’ of the spectricityvectors. In most cases, the specific orientation properties of theobject and its surface elements is an initial unknown, but normalmorphological reasoning suggest that if one is taking a picture of apear, then a de facto sampling of patches will see patches ranging fromthose aligned with the camera axis to those ‘at the edges’ andperpendicular to the camera axis, then all surface normal in betweenthose two. Purely circular objects like billiard balls have quitepredictable distributions of those surface normal whilst heavily foldedhot green peppers may not. The overall point relative to ‘errormitigation’ for individual patch spectricity measurements is that2-dimensional and/or ‘spatial/structural’ information of the underlyingimage itself can assist in sleuthing probable surface normal estimatesfor given patches, then using these estimates again as effective‘labels’ on measured spectricity vectors. A large fuzzy histogram bincan be set around surface patches with ˜45 degree angles plus or minus30 degrees for example, with such wide margins still being useful tohigher level object recognition algorithms. Some information/estimateswill be better than none, especially when it is realized that moderncameras obviously now have millions of pixels which effectively breakdown into thousands and hundreds of thousands of patches if one views‘patches’ in the roughly 10 by 10 pixel sense.

This line of discussion brings us to the following point: The path andcurvature properties of spectricity vectors can, with proper scrutinyand attention to details, be informationally complete descriptors forobject morphology. To illustrate the point, the following is methodbased on this technology for obtaining surface structure of objects:

First using a configuration of the type described in this disclosure, alight source—camera pairing is used to capture images;

then a programmed device or hardware logic:

obtains the spectricity vectors of an object from some fixed viewpointfrom these images,

calculates the curvatures and paths of those N-D spectricity vectors asa function of the 2 dimensions of the camera's pixels, then

maps those resulting paths/curves in N-D space to surface normalestimates of objects.

The surface normal estimates provide a feature characterizing anobject's surface, which may be combined with other features for objectrecognition. This can be leveraged in 2D and 3D object recognitionmethodologies as another identifying feature, such as in the Bag ofFeatures based approaches referenced below.

This method is applicable for objects that have ‘modest’ anddemonstrably semi-uniform spectral properties across its surface. Thischaracterization of object surface is useful for a variety ofapplications including, for example, object recognition purposes amongothers. Aspects of these path/curvature properties will be seen insubsequent disclosure sections, starting with the next section onSpatio-Spectricity Produce Recognition.

Spatio-Spectricity Object Recognition

In U.S. Pat. No. 6,363,366, incorporated herein by reference, entitled“Produce Identification and Pricing System for Check-outs,” inventorDavid L. Henty describes a system which posits that many types ofproduce can be distinguished based on unique spectral signatures.

This task of distinguishing produce can be augmented by employingmethods of this disclosure to extract additional distinguishingcharacteristics and integrate them tightly with feature vectortechniques used in 2D image and 3D object recognition. One advance, forexample, is the use of the above described technique to characterize anobject's surface from spectral image data, and use a combination ofsurface features and spectral signature to discriminate and/or identifyobjects.

Henty's disclosure did not address a number of challenges associatedwith identifying produce that are yet to be adequately addressed. Whileone would hope that one specific type and ripeness of banana has ameasurably unique ‘spectral signature’ all to itself, much as a stableformula for a specific dried house paint might have, the reality is thateven just on the surface of a single banana, measured in alaboratory/darkroom setting, one finds an extraordinary breadth of notjust ‘spread’ in those signatures but also complicated N-dimensionalstructure. The next day the same banana, still in the laboratory, moveson to new though certainly highly related structure in signaturedistributions over its surface. Add now the banana in the bunch rightnext to it, and several more, over several days, and both the globalspreads as well as the specific N-dimensional structures dictate thatmore sophisticated feature vector extraction is needed to enableclassification of such objects.

The techniques described in this document may be leveraged to derivefeature vectors from spectricity vectors, in combination with otherimage features used for 2D image and 3D object recognition.

In one class of classifier technology, our classifier methods uses theprincipal components of the error ellipsoids of these spreads toformulate a spectral image based feature vector for discriminatingproduce.

To provide a more powerful discriminator, our classifier embodimentsinvoke a higher level of discriminant blending which—as with RGBchromaticity long before it—places higher dimensional spectricitycoordinates into two dimensional SIFT/SURF/edge discriminant imagerecognition disciplines. As one example, the two dimensional curve andpath behaviors in N-D spectral space that are native to singularinstances of a given fruit or vegetable are the characteristicstructures that are submitted to late-stage discriminant routines.

We describe these techniques further below and in related disclosures inprocess.

Omnidirectional Lighting (Diffuse or Directional LED Configurations)

For must applications, it is desired to create uniform lighting acrossthe field of view. For example, in implementations used to experimentwith various LED configurations, we have sought to configure the LEDlight sources to provide nearly uniform lighting across a typical sheet(8.5×11 inches). To do so, we configure LEDs to provide diffuselighting. As described herein, while suitable for some applications, thelight field may not be sufficiently uniform for others. In that case,the various techniques describe in this disclosure for correcting forthis effect may be employed.

For some applications, additional shape and structural characteristicsof objects can be extracted from images of them by pulsing withdirectional and non-directional light sources. These variations in lightsources may be used to more accurately reveal object edges and redressshadows.

User Interface

The technologies of this disclosure can be used to development usefuluser interfaces that enable users to visualize and discriminatecharacteristics of objects captured by a camera. In one arrangement, theuser interface is implemented in a programmable computing device with acursor control and display. The display depicts images of objects, suchas produce, captured using the above techniques for deriving spectricityvectors. 2D color images of the N-D spectricity images are generated bymapping N-D spectricity vectors to a 2D color image space. Then, withinthis display, the user can select pixels within an object of interest.In response, the computing device calculates a distance metric and thendetermines from the N-D dimensional spectricity data of that pixel andall other pixels, which pixels fall within a threshold distance of theselected pixels' spectricity vector. A new image is then generatedhighlighting pixels in a visibly distinguishable color that fall withinthe distance metric. One such distance metric for N-Dimensional vectorspace is a Euclidian distance, but there are many other distance metricsthat may be substituted for it.

This approach can be further extended to create augmented reality (AR)type user interfaces superimposed on video captured of objects. ARapplications process a video feed, recognize objects within a scene andoverlay graphical UI elements over the video feed as it is displayed onthe user's device. The above UI paradigm, extended to the AR context,and with feature recognition automated, provides a foundation for avariety of AR type UI features. These UI features take advantage of thediscriminating and identifying power of N-Dimensional spectral contentwith the ability to map graphical elements specifically to color imagepixels in the 2D display. Thus, as the user views objects in a scene,objects identified or distinguished by their N-D spectral vectors havetheir pixels highlighted or otherwise augmented with graphic overlaysmapped to screen locations.

Classifiers

The process of constructing a classifier involves selection of featuresthat most effectively discriminates among the class of objects sought tobe classified. There are a variety of ways to select features, includingmanual and empirical based techniques, machine learning methods thatutilize supervised or unsupervised learning, and combinations of theseapproaches. See, for example, our patent application on machine learningtechniques: 61/880,798, entitled Learning Systems and Methods, which ishereby incorporated by reference.

In some spectral imaging applications, principal component analysis hasbeen employed to reduce the feature space and determine features, e.g.,spectral bands used to discriminate objects. In one application, forexample, PCA was used to determine spectral bands for discriminatinggrapevine elements. See: Fernández, R.; Montes, H.; Salinas, C.; Sarria,J.; Armada, M. Combination of RGB and Multispectral Imagery forDiscrimination of Cabernet Sauvignon Grapevine Elements. Sensors 2013,13, 7838-7859.

Extensions to Hyper-Ellipsoid Regions within Multi-Dimensional Space forClassification

As noted above, spectral image data may be mapped into feature vectorspace defined in terms of a hyper-ellipsoid region in multi-dimensionalspectral space where the distinguishing spectral characteristics of anobject maps into. One method based on this concept is as follows:

Take an object that one seeks to classify; select N patches of spectralimage of that object (e.g., N 11 by 11 pixel patches), fit ahyper-ellipsoid around the region of those patches in N-D spectricityspace, expand that region to encompass patches while avoiding overlapwith regions for distinct objects.

Various feature quantization and binning strategies may be used to mapspectral image data into a feature vector used to identify ordiscriminate it relative to other objects. Two examples of suchstrategies are Vector Quantizer and t-SNE based methods.

Spectra Identification (“ID”) Imaging Modalities

This document describes a class of embodiments of multispectral imagingtechnology that can be used in a variety of applications, leveragingmachine vision and/or machine learning, as appropriate. By exploitingthe spectral dimension, this class of technology provides improvedperformance in such applications.

One imaging modality is the use of multiple LEDs of varying spectralcharacteristics for multiple exposures of the target of interest. Thesemultiple LEDs can also be optionally augmented by multiple filters ofdifferent spectral characteristics (for example, the traditional RGBbayer filter pattern). The multiple exposures, including optionalexposures of the ambient environment with no LED, can be combinedmathematically to yield a spectricity image that is analogous to theconcept of two-dimensional chromaticity.

There are several alternative imaging modalities that may be preferablefor some applications. These include devices employing alternative waysto gather spectral images. One alternative is to use a hyperspectralimaging camera. One type of camera offered by Specim, of Oulu Finland,employs an objective lens in which light is first focused onto a narrowslit and then collimated through a dispersive element. This dispersiveelement has the effect of splitting the light into a series of narrowspectral bands that are then focused onto an area-array detector. Inthis way, the spectral properties of the single line of light at narrow,contiguous bands are captured. Since the cameras image single lines oflight at a time, they must be operated in a push-broom or line scanfashion in which either the object to be measured is moving across thefield of view of the camera, or the camera is moved across the field ofview of the object. In this manner, a hyperspectral cube can be createdthat represents a stack of 2-D images, each of which contains specificinformation about individual frequency bands.

Advances have been made in replacing traditional optics of this approachwith on-chip optics and a tunable micro-electromechanical system. Inparticular, IMEC of Lueven, Belgium has developed sensors based on thistype of approach. In one spectral imager design, the narrow slit andcollimator become optional and the dispersive elements and focusing lensare replaced by an optical fixed wedge structure that is post-processedonto the imager sensor. In another design, the slit and collimator arealso replaced with a tunable micro-electromechanical system (MEMS), suchas a MEMS implementation of a Fabry-Perot Tunable Optical Filter (TOF).Other types of MEMS based TOFs include, for example, Mach-Zehnder (MZ)filters, and Grating-based filters. When a TOF is used in conjunctionwith an objective lens, the other elements can be replaced, resulting ina faster, more compact, frame-based hyperspectral camera. For instance,such devices can operate at approximately 10 k lines/s compared with the0.2 k to 1 k lines/s with traditional optics approaches. The line scanhyperspectral imager from IMEC, for example, scans 100 spectral bands inthe 600-1000 nm wavelength range.

TOFs may be configured on an array of pixel elements of an image sensor(e.g., CCD or CMOS) such that they provide an optical band pass filtercorresponding to a group of pixel elements. For example, the TOF may beimplemented as a stepped wedge positioned across groups of pixelelements.

Another complementary optical element for a portion of the image sensoris a prism for sub-dividing light at different wavelengths tocorresponding pixel elements. A prism is particularly useful forsplitting incoming IR into an IR wavelength per pixel element on thesensor. In one configuration, for example, a prism is positioned over arectangular slice of a sensor surface adjacent the TOF elements. Thisenables the corresponding pixel elements to each capture a correspondingwavelength within the IR range. This type of IR sampling has theadvantage that it allows the sensor to get detailed IR sampling perwavelength. Various types of plastics are transparent to IR. Thus, inthe retail setting, the IR portion of the sensor can be used to samplecharacteristics of an item through the plastic packaging or wrapping,such as produce items or meats. For more on use of optical techniquesfor imaging through plastic and other types of materials transparent toIR, please see 20130329006, which is incorporated by reference hereinand provides imaging techniques useful and compatible with those in thisdisclosure.

The above line scan approach can be employed along with additional imagecapture elements to capture spectral images in 2 spatial dimensions. Forexample, in one embodiment, the line scan imager is combined withscanning mirrors to capture full images. In other embodiments, it iscombined with strobed or sequenced bandwidth controlled illumination.

Another alternative is to employ Transverse Field Detector (TFD)sensors, with tunable spectral response to provide spectral images. Thistype of image sensor is described in “The Transverse Field Detector: ANovel Color Sensitive CMOS Device”, Zaraga, IEEE Electron Device Letters29, 1306-1308 (2008), “Design and Realization of a Novel Pixel Sensorfor Color Imaging Applications in CMOS 90 NM Technology”, Langfelder,Electronics and Information Department, Politecnico di Milano, viaPonzio 34/5 20133, Milano, Italy, 143-146 (2010), and U.S. PatentPublication No. 2010/0044822, the contents of which are incorporatedherein by reference. These documents describe a TFD which has a tunablespectral responsivity that can be adjusted by application of biasvoltages to control electrodes. In a three channel TFD, each pixeloutputs signals for a red-like channel, a green-like channel, and ablue-like channel. Symmetric biasing is applied, such that related pairsof control electrodes each receive the same bias voltages.

Pixel measurements can also be obtained for additional or other spectralbands. A TFD with more than three channels can be provided by applyingan asymmetric biasing to a symmetric TFD pixel and increasing the numberof spectral channels in the same pixel area. By applying asymmetricbiasing, each of five electrodes of the TFD pixel could receive adifferent bias voltage, thereby providing for five channels that caneach be tuned to different spectral sensitivities.

In some of these image sensors, the spectral responsivity is tunableglobally, meaning that all pixels in the image sensor are tuned globallyto the same spectral responsivity.

In some others of these image sensors, the spectral responsivity istunable on a pixel by pixel basis or a region-by-region basis. Biasvoltages are applied in a grid-like spatial mask, such that the spectralresponsivity of each pixel is tunable individually of other pixels inthe image sensor, or such that the spectral responsivity of each regioncomprising multiple pixels is tunable individually of other regions inthe image sensor.

Another alternative is an image sensor preceded by a Color Filter Array(CFA) with a tunable spectral response. A CFA may be used with a sensorhaving a constant spectral response, or in combination with one having atunable spectral response, such as a TFD sensor. One example of atunable color filter array described in U.S. Pat. No. 6,466,961 byMiller, “Methods for Adaptive Spectral, Spatial and Temporal Sensing forImaging Applications”, the content of which is incorporated herein byreference. This document describes an imaging assembly comprising acolor filter array which precedes an image sensor whose spectralresponsivity is constant, but in which the color filter array itself hasa tunable spectral responsivity that can be adjusted by application ofbias voltages to control electrodes. Each array element thus filterslight incident on corresponding pixels of the image sensor, and theimage sensor thereafter outputs signals from which a red-like channel, agreen-like channel, and a blue-like channel, can all be derived for eachpixel. In the case of a color filter array with temporal sensing, thechannels for each pixel may be output sequentially, one after the other.In the case of a color filter array with spatial sensing, the channelsfor each pixel may be output simultaneously or nearly so, althoughdemosaicing might be required depending on the geometry of the colorfilter array.

A spatial mosaic can be constructed using tunable color filters on topof individual imaging sensors. A Bayer-type mosaic provides colorfilters tuned to provide three channels distributed spatially. Thenumber of channels can be increased beyond three by tuning color filtersto provide four, five or more channels distributed spatially. There is atrade-off between spectral resolution, which is determined by the numberof channels, and spatial resolution. However, by increasing the numberof pixels of an image sensor, the visual effect of loss in spatialresolution can be minimized. An increased complexity of the spatialmosaic typically requires more complex demosaicing procedures as well aslarger spatial filters for demosaicing.

In some of these color filter arrays, the spectral response is tunableglobally, resulting in a situation where corresponding channels for allpixels in the image sensor are tuned globally to the same spectralresponsivity.

In some others of these color filter arrays, the spectral responsivityis tunable on a pixel by pixel basis or a region-by-region basis. Biasvoltages are applied in a grid-like spatial mask, such that the spectralresponsivity for each pixel is tunable individually of other pixels, orsuch that the spectral responsivity for each region comprising multiplepixels is tunable individually of other regions.

FIGS. 63-64 illustrate some example embodiments of these types ofmulti-spectral image sensors. To provide a baseline from whichadditional embodiments are constructed, FIG. 63 is a diagramillustrating an image sensor comprising an array of pixel elements.

FIG. 64 is a diagram illustrating top and perspective views of an imagesensor with optical band pass filters, each for a band of wavelengthsλ_(n) (n being a number representing a band of wavelengths), arranged onan array of pixel elements. This is just one example of a spatialconfiguration of optical band pass filters to pixel elements on thesensor, and spatial configuration may vary. One reason for varying theconfiguration is to complement additional optical elements, such aslens, mirrors and prisms, light source position, type andstrobing/sequencing, and object scanning methodologies, to obtain adesired 2 or 3 dimensional spatial array of pixel samples with desiredresolution of spectral information per unit area/volume of the field ofview.

These approaches may be combined with additional elements to capturespectral channels for each pixel in a 3 dimensional array of pixels (x,y, z coordinate space, adding depth). For example, the 1 spatialdimension (line scan) or 2 spatial dimension imaging modes describedabove may be combined with a micro-lens for plenoptic vision. Thisyields additional spectral data by slicing the N-D spectricity vectordata at differing depths of field. For applications involving scanningobjects with translucent surfaces, this enables the imaging device tocapture spectral response at depths below the immediate surface of theobject. Many biological objects are somewhat translucent, especially toIR—skin, fruits, vegies, etc., and the spectricity vectors for eachpixel captured at varying depths provide additional information todiscriminate and identify objects.

In addition to spectral and spatial information, yet another type ofinformation that may be measured is polarization using a polarizationimage sensor. See, for example, V. Gruev and T. York, “High ResolutionCCD Polarization Imaging Sensor,” in International Image SensorWorkshop, Sapporo, Japan, 2011; and US Patent Publications 20130293871and 20070241267, which are hereby incorporated by reference herein. In20130293871, Gruev stacked the photodiodes for different wavelengths ofabsorption at different depths for each pixel under thepolarization-specific filters. This work by Gruev et al. providesexamples of polarization imaging sensors.

Other forms of polarization imaging devices may be constructed usingalternative and complementary techniques. One approach is to employpolarizing filters on the light source and camera, with the filtersselected sequentially for image capture such that a polarizer at a firstdirection is selected for the light source, and images captured througha polarizer at the camera at the same direction, plus or minus 45 and 90degrees. Using this approach, polarization measurements can be made forimages captured with several different combinations of light source andcamera polarizers.

One motivation for measuring polarization (also referred to aspolarimetric information) is to discern additional properties of anobject being imaged to identify or classify it. Polarization of lightcaused by reflection from materials contains information about thesurface roughness, geometry, and/or other intrinsic properties of theimaged object. Polarization can be used in ellipsometry to measurematerial properties and stereochemistry to measure specific rotation.Ellipsometry is an optical technique for investigating the dielectricproperties (complex refractive index or dielectric function) of thinfilms. Ellipsometry can be used to characterize composition, roughness,thickness (depth), crystalline nature, doping concentration, electricalconductivity and other material properties. It is very sensitive to thechange in the optical response of incident radiation that interacts withthe material being investigated. The measured signal is the change inpolarization as the incident radiation (in a known state) interacts withthe material structure of interest (reflected, absorbed, scattered, ortransmitted).

In stereochemistry, the specific rotation ([α]) is an intensive propertyof a chemical compound, defined as the change in orientation of theplane of linearly polarized light as this light passes through a samplewith a path length of 1 decimeter and a sample concentration of 1 gramper 1 millilitre. It is the main property used to quantify the chiralityof a molecular species or a mineral. The specific rotation of a purematerial is an intrinsic property of that material at a given wavelengthand temperature.

In applications for classifying produce, the polarization properties ofsugar molecules may be used. All natural plant sugars are achiral—thatis they have one particular handedness of molecule (left or righthandedness). Thus, these sugars will rotate polarized light. Some othermolecules within the fruits and vegetables will also have thisattribute. Concentrations and molecule types have different rotationamount and this varies with wavelength too. Reflection of polarizedlight within the outer layers of a produce item show rotation, andvarying rotation with wavelength, the composition and concentrations ofchiral molecules in that layer, the total optical path-lengths for eachwavelength. This polarimetric information provides clues on ripenessavailable as different sugars are formed or broken down (variousreactions catalyzed by enzymes within the fruit or hydrolized ormetabolized by decay/bacteria/etc.).

Another application of polarizers is to be able to enhance image samplecapture by separating specular and diffuse light, such as that reflectedfrom a scene or object being imaged. The specular reflection is stronglypolarized, whereas diffuse reflection is not. The specular reflectionfrom the surface of a package or wrapping or plastic bag on produce, forexample, is reduced by using polarizers and post processing to detectand reduce specular reflection from the sampled image, includingspectral image data. This post processed image is then submitted to ourclassifiers for classification. The polarizers allow specular reflectionto be detected by correlating the similarly polarized sampling of lightacross polarizers within the imaging arrangement. Specular reflectionwill have common polarization, whereas diffuse light will not. Thus, itcan be detected by determining correlation among polarization of pixels.

Plenoptic capability in the camera enables the sampling and postprocessing from the plenoptic camera to provide image views at differentview angles, and thereby obtain pixels sampled from view angles atdifferent angles relative to the Brewster's angle. For each of differentview angles, the specular reflection is ascertained by post processingof the polarimetric information associated with pixels using the abovedescribed technique of correlating polarimetric information across thepixels. Subsequent diagrams depict examples of sensors with bothpolarizing and plenoptic capability, enabling capture of pixels thatimage an object at different view angles and orientation of polarizer.

Another way to reduce specular reflection is to illuminate an objectusing a light source where the angle of light relative to the image maybe changed, enabling capture of different frames or scans with differentlight angles from the light source to the object. One example is toconfigure LED light sources in ring or other spatial arrangement inwhich the light angle to the object is sequenced by selective pulsing ofthe LEDs.

In these types of arrangements, specular reflection impacts can bereduced on subsequent recognition post processing by selecting pixelsfor input to the post processing captured under modes, such asplenoptic-enabled varying view angle, or pulsed light at varying anglesto the object, where specular reflection is measured to be low via theabove correlation based technique.

These techniques for sensing and post-process computational exploitingof polarization information may be used in combination with spectralimaging techniques described above. For example, Guev's high resolutionpolarization imaging sensor provides specific orientations of polarizersover each pixel. This type of imaging structure can be used incombination with color imaging, and spectral image capture described andreferenced in this document. One approach is to illuminate an objectwith switched polarized light sources (on/off, or polarization angleswitch (or circular left/right), colors, etc.), and then obtain theadditional dimension of information provided by calculating polarizationrotation in the image (by wavelength and amount). This type of imagingassembly and method could, of course, be combined with the low-costhyper-spectral imager camera using the lithographically producedFabry-Perot filters, or other means of spectral capture (e.g., TFD, CFA,strobed light sources, etc.).

FIGS. 65-71 illustrate additional embodiments of imaging sensorconfigurations that have polarizer and/or plenoptic capture capability,which may be used in combination with a variety of the multi-spectralcapture techniques described above.

FIG. 65 is a diagram illustrating top and perspective views of an imagesensor with a polarizer (e.g., for measuring one of four orientations 0,45, 90 and 135 degrees) over each pixel element. This may beimplemented, for example, according to the work of Gruev at al. onpolarization sensors cited above.

FIG. 66 is a diagram illustrating top and perspective views of an imagesensor with a polarizer per pixel element, and optical band pass filterper 2D block of pixel elements. This is one example configuration ofcombining polarimetric capture with multispectral capture using opticalfilters on the sensor. As an alternative to these types of opticalfilters, other multi-spectral capture may be used instead, or incomplementary fashion, such as strobed light sources (e.g., LEDs ofdifferent wavelengths), TFD sensors, or other technologies describedherein.

FIG. 67 is a diagram illustrating a side view of an image sensor andlens configuration, together forming a plenoptic camera. As noted in thediagram, this particular positioning of a main lens and microlens arrayprovides a focused plenoptic camera with real image from main lens infront of microlens array. Alternative embodiments have a virtual imagefrom the main lens behind the microlens array, or the microlens arraylocated in the plane of the main image.

The plenoptic capability enables the image sensor configuration tocapture multiple views of a scene or object from slightly different viewangles. For example, the 2D array of pixel elements under each microlenscaptures a sub-image of the scene. This provides the capability tocapture sub-images of an object being imaged at the pixel elements beloweach microlens, with each sub-image providing a different spectraland/or polarimetric sampling of the object.

The plenoptic capability also enables the derivation of pixel samplevalues at different depths (as noted above) using computationalphotography techniques. This provides the capability to measure spectraland/or polarimetric information at depths above, at and below thesurface of an object being imaged (in other words, 3D image capture ofspectral and polarimetric information).

FIGS. 68-71 illustrate various options of imaging configurations, andteach many additional variants that can be made by interchangingcomponents.

FIG. 68 is a diagram illustrating a side view of an image sensor havingoptical band pass filters on the sensor, followed by a microlens array,where the filters are positioned to coincide with a correspondingmicrolens array element such that there is one filter per sub-imageobtained through the positioning of a main lens relative to themicrolens array as shown. This is an example where each sub-imageprovides a different spectral band corresponding to the band of theoptical band pass filter coinciding with the microlens above it.

FIG. 69 is a diagram illustrating a side view of an image sensor likethe one in FIG. 68, but further adding a layer of polarizers between theoptical filter elements and microlens array. This adds polarimetriccapture capability to the configuration of FIG. 68. Within eachsub-image corresponding to a microlens and filter pair, the polarizersprovide polarimetric capture at different orientations, similar to theexamples depicted earlier. The orientations of the polarizers can bevaried within a sub-image area, or may be the same across eachsub-image, yet different from one sub-image to another.

FIG. 70 is a diagram illustrating a side view of an image sensor likethe one in FIG. 68, but with the alternative of having multiple opticalband pass filters per sub-image. This configuration provides thecapability to capture multiple different spectral bands within eachsub-image. Sub-images may be combined to provide multiple spectral bandsper common pixel location within each sub-image.

FIG. 71 is a diagram illustrating a side view of an image sensor likethe one in FIG. 69, but without the optical band pass filters. Thespectral capture may be achieved using technology other than the opticalband pass filter technology mentioned, such as TFD or strobing of lightsources at different spectral wavelengths.

These various imaging modalities may be implemented in variety of devicetypes. These types include general purpose imaging devices, such ascameras and scanners, where multispectral capture modes are providedamong dedicated camera options. These device types also includemultifunction devices such as mobile devices and computers withintegrated cameras and light sources (e.g., smartphones, tablets,personal computers, etc.). Another device type is a special purposedevice, such as barcode scanning equipment, machine vision systems,medical imaging tools, etc.

Tailoring the Classification Methods to the Statistics of Classes

The Spectra identification approach can be used to classify observationsof a plurality of classes. Preferred implementations of classificationalgorithms will in many cases depend upon characteristics of the classesto be identified, as different collections of classes will be more orless amenable to identification using different types of algorithms andtechniques.

A main influence on the type of classification algorithms which are mostuseful is the statistics that surround the different classes to beidentified. Here, statistical variation within all the objects of aclass is of interest, as well as statistical variation between differentobservations that may be made of a single sample or individual to beidentified. Of course, if the statistical variation is far wider betweenclasses than within classes, the classification task is much easier.However, in many cases, the observed distributions between classes arenot trivially separated. Additional statistical issues must then beconfronted in the design of a classifier based on limited training data;the well-known tension between under-fitting and over-fitting is at basea statistical problem.

It is useful to construct a simple “taxonomy” of the statisticalvariation that can be seen within classes. Specific observation andclassification algorithms can then be brought to bear on theclassification problem based upon the statistics in the classes ofinterest.

1. Impulsive sources. Some spectral sources are especially well-defined,such as the emission spectrum of sodium. In terms of spectricity, thesesources can be best represented as single points within themultidimensional spectricity space. In the case of sodium, there areclear physical explanations that can be identified to explain thespecific spectrum.

2. Near-Impulsive sources. Pantone™ ink spot colors are sources that canbest be represented as single spectricity “impulses”, even though theremay be some (relatively limited) variation among samples. Variationamong different samples of the same color can be ascribed variously todifferences in base ink mixing proportions, age, and fading due tosunlight, etc. Classifier designs can take into account the relativemagnitudes of variation about an ideal impulsive characteristic that aredue to variation among different individual examples of members of theclass versus variation within a single sample being classified.

Classifiers for impulsive and near impulsive sources can be relativelysimple, compared with classifiers for the following types of sources.

3. Distributed sources. For some sources, there is significant variationeither between different individuals within a class, or within a singlerepresentative of the class, or both. An example of this type of sourcewould be apple varietals. Each type of apple (Pink Lady, Pinata,Ambrosia, etc.) can exhibit a range of different colors and, therefore,spectricities. In contrast to the impulsive sources, a distributedsource can be represented with a non-impulsive marginal probabilitydistribution in the N-dimensional spectricity space.

Specific classification strategies can be used to deal with difficultiesof distributed sources.

4. Sources with memory. Some distributed sources have additionalstatistical complexity that cannot be captured through a marginalprobability representation. This is true for the previous example, thatof varieties of apples. In other words, looking at the probabilitydistribution of N-dimensional spectricities of a single pixel of animage of a Pinata apple does not capture the full picture. Put anotherway, the distribution of the spectricity of one pixel in the image of aPinata apple is not independent of the spectricities of nearby pixels.

A random process with memory always has less entropy than a memorylesssource; a corollary of sorts is that memory should be an exploitablecharacteristic that can provide identical or improved classificationperformance over classifiers that do not exploit source memory.

Strategies for Dealing with Distributed Sources.

1. Visualization. Being able to visualize N-dimensional spectricitydistributions of the classes to be identified is invaluable. Ofimportance here are dimensionality reduction techniques that canpreserve enough of the N-dimensional structure in a two or threedimensional representation.

One method that has been found useful is t-Distributed StochasticNeighbor Embedding (t-SNE).

t-SNE Based Methods

t-SNE methods provide an effective tool for visualizingmulti-dimensional data sets, such as our N-D vectors in lowerdimensions, such as 2D or 3D representations that humans can analyze.For example, such a tool enables us to visualize the extent to whichspectral N-D vectors of image patches of different objects (e.g.,produce items) map to distinct clusters in a dimension we can visualize(2D or 3D space). This assists in the design of classifiers, forexample. The next paragraphs provide an overview, and then we describefurther applications of this tool with our technology.

See, L. J. P. van der Maaten and G. E. Hinton. Visualizing Data usingt-SNE. Journal of Machine Learning Research 9 (November): 2579-2605,2008). T-SNE represents each object by a point in a two-dimensionalscatter plot, and arranges the points in such a way that similar objectsare modeled by nearby points and dissimilar objects are modeled bydistant points. When t-SNE software constructs a map using t-SNE, ittypically provides better results than a map constructed using somethinglike principal components analysis or classical multidimensionalscaling, because:

(1) t-SNE mainly focuses on appropriately modeling small pairwisedistances, i.e. local structure, in the map, and

(2) because t-SNE has a way to correct for the enormous difference involume of a high-dimensional feature space and a two-dimensional map. Asa result of these two characteristics, t-SNE generally produces mapsthat provide clearer insight into the underlying (cluster) structure ofthe data than alternative techniques.

In one embodiment, we used t-SNE to map 45 dimensional spectricityvectors into a 3D space for visualization. The approach is:

i. Compute 10 principal components of a spectricity data set for anobject

ii. Set up the data for the t-SNE software to map the spectricity datainto a 3D representation by setting constraints at each end of theprincipal component axes. For this embodiment, we set these constraintsto correspond to an opposing pair of vertices of a dodecahedron in 3Dspace. There are a total of 20 ‘sphere constraints’ which areartificially placed well outside the data blob zone but exactly on thefirst 10 principal component axes of the data itself, one each at thetwo poles of each principal component. The 3D projections of theseconstraints are initially set to the 20 vertices of the dodecahedron,but then the t-SNE software is free to move them about using itsalgorithms.

iii. Execute the t-SNE software to map the spectricity data to the 3Dspace with these constraints. We observed that this approach causes theprincipal components and associated data samples to move about in the 3Dspace, yet still provide a 3D visualization of the spectricity vectors.

This technique allows us to visualize 45 dimensional spectricity vectorsfor different classes of objects to see how the vectors differ fordifferent classes. This provides clues for classifier design, as well asa means for users to visualize and discriminate objects based on theshape of the mapped data of an object.

One application of this technology is to use it in the derivation ofbins that can be used in recognition methodologies such as vectorquantization as well as Bag of Features, in which feature vectors forspectral data input are mapped to bins. These approaches are describedelsewhere in this document, including in the section on vectorquantization and in sections relating to Bag of Feature approaches.

Another application is the design of UIs for applications, like smartphone mobile applications that are configured to compare objects andillustrate how similar they are in multi-dimensional space through a 2Dor 3D depiction on the display of the mobile device.

2. Classification. As an example of methods for dealing withclassification of distributed spectricity sources a simple example ofclassification of apple varieties is described.

Samples of 20 apples each of three different varieties of apples (PinkLady, Pinata, Ambrosia) were used. A database was constructed with eachapple represented by four images of different areas of the apple. Imageswere taken at a fixed distance, with each apple placed on a board with a1.5 inch circular hole, and the camera imaging the apple from belowthrough the hole. Each image consisted of 16 exposures, including 15different LED exposures and a reference ambient exposure. Each image wassegmented to remove non-apple areas of the images. A color camera wasused, and spectricity values were calculated for each pixel in theapple-segmented image.

Experiments were run by randomly assigning 10 apples from each class toa training set, and using the remaining apples as a test set. Thisprocess was repeated many times to arrive at average expectedperformance results.

a. Vector Quantization Based Methods.

This section immediately addresses the task of using spectralmeasurements from a small number of image bands (typically between 5 and15) to classify (identify) produce items. It is more generallyapplicable to a wider array of problems, including different 2D imagerecognition and 3D object recognition applications. A smaller or muchlarger number of spectral bands are easily accommodated. The techniquescan also be adapted to a variety of other continuous or many-valuedcharacteristics of produce that may be measured. Finally, these ideasmay be used to classify items outside of the field of produce.

Vector Quantization

Because we are dealing with multi-dimensional spectral measurements, thevector quantization approach will be used. Vector quantization is awell-studied technique for lossy data compression, and it has also beenproposed for use in classification applications.

See, for example:

-   -   Pamela C. Cosman, Robert M. Gray, Richard A. Olshen, Vector        quantization: clustering and classification trees, Journal of        Applied Statistics, Vol. 21, Iss. 1-2, 1994    -   Supervised learning systems, based on vector quantization        systems, are sometimes referred to as Learning Vector        Quantization (LVQ) systems, and one can learn more about such        systems by reviewing literature on LVQ.    -   Another example of a VQ based learning system is referred to as        Classified Vector Quantization, and such an approach is        described in Bailing Zhang, Classified Vector Quantisation and        population decoding for pattern recognition, International        Journal of Artificial Intelligence and Soft Computing, Volume 1        Issue 2/3/4, July 2009, Pages 238-258.    -   The above are but a few examples of background and supporting        literature on the design of VQ based systems that one may refer        to in implementing our methods or variants of them.

An n-dimensional vector quantizer (VQ) maps n-dimensional sample vectorsto quantized codebook vectors. A VQ consists of a codebook C=(c1, c2, .. . cM) of M n-dimensional vectors, and a partition P on then-dimensional space so that each codebook vector has a correspondingcell of P. A source vector v is encoded by representing it with theindex of the cell of P which contains v. If a VQ codebook contains 2^mcodebook vectors, then it can quantize a source of n-dimensional vectorsat a rate of m/n bits per sample. A VQ is designed (trained) using atraining set of n-dimensional vectors taken from a distribution whichapproximates the source.

Usually, the squared error metric is used, so that the codebook vectorchosen to represent a source vector is the codebook vector with smallestEuclidean distance to the source vector. For classification purposes,squared error may be appropriate, or certain other measures may be used.There are alternatives for an appropriate measure of distance orsimilarity for training and classification. Techniques have beendeveloped which adapt a parameterized distance measure in the course oftraining the system, see e.g., P. Schneider, B. Hammer, and M. Biehl.Adaptive Relevance Matrices in Learning Vector Quantization, NeuralComputation 21: 3532-3561, 2009, which is hereby incorporated byreference herein. For further information, also see the references citedtherein.

Design and encoding complexity of general VQs increase quickly withincreasing dimension and/or quantization rate. The limiting performanceof a set of VQs with increasing dimension satisfies the rate/distortionbound of a given source.

Tree-Structured Vector Quantizers (TSVQ)

TSVQs are a simplified class of VQs that provide sub-optimalperformance, but have a lower complexity of training and encoding. ATSVQ consists of a set of simple VQs of the same dimension which satisfya tree structure. In the simplest case, that of a binary TSVQ, each ofthe component VQs has a codebook with two code vectors. Thecorresponding tree structure is a binary tree, with each component VQoccupying a single node of the binary tree. Source vectors are quantizedby first quantizing them with the root component VQ. Then, based onwhich code vector best represents the source vector, the source isquantized using the corresponding first level descendent VQ. Thisprocess is repeated until the source is quantized using a leaf node VQ.For a balanced binary tree of m levels, the quantized version of asource vector is given by the binary vector specifying the path from theroot of the tree to the final quantized codebook value. The resultingcompression rate is m/n bits pre sample.

Training such a TSVQ is a recursive process. First, the root node VQ istrained. The result is a VQ that partitions the training set of vectorsinto two training subsets, one for each codebook value. Each of thesetraining subsets is then used to train the corresponding component VQ inthe tree structure. At the end of this process, there are four trainingsubsets. This process is repeated, for a balanced tree TSVQ, until thedesired number of levels in the tree have been constructed.

Classification Using TSVQs

If the spectricity values in the training set are quantized using avector quantizer, each class of items (e.g., apples in our example) willimpose a corresponding probability distribution (probability massfunction (pmf)) across the voronoi regions of the quantizer, with aprobability mass associated with each voronoi region. This distributioncan be characterized and used to help classify the test samples, basedupon the quantized values of the pixel spectricities in the testsamples. The VQ pmf is used, rather than the raw N-dimensionalspectricity pmf of the training set because each component of aspectricity vector was represented with 16 bits of precision, and thetraining pmfs of each apple type would severely overfit the truespectricity pmf of each class.

VQs in general can be used for classification by associating a classwith each codebook vector. As long as the members of classes tend to beclose to one another for some convenient distance measure, these memberswill tend quantize to the same codebook vectors. The simplicityadvantages of TSVQ can be used to improve the simplicity of theclassification task, as well as possibly providing some additionalflexibility; the techniques to be described will also apply to otherforms of VQs.

Training a TSVQ for classification is an exercise in unsupervisedlearning. We can augment the normal TSVQ training process by associatinga class tag with each training vector in the training set. So, forexample, we could have training data for 20 varieties of produce(jalapeno, cucumber, banana, etc). For each variety we obtain a quantityof 10 items. Then, for each of the 200 items, we take ten multispectralimages, each with 8 spectral bands. For each multispectral image, weapply a simple averaging filter and then randomly select 108-dimensional pixel vectors. In total there are 20 varieties×10 items×10images×10 vectors=20000 vectors, each with a tag identifying thecorresponding produce variety.

The TSVQ is trained in the normal way, keeping the tag classassociations in the construction of each training subset. In addition,we associate a probability distribution, called the estimateddistribution, with each codebook vector of each component VQ (at alllevels of the tree). This distribution represents the distribution ofclass tags within the sub-training set of training vectors that arequantized to that codebook vector. The TSVQ is designed in an unbalancedtree such that, at the leaf codevectors, each corresponding trainingsubset has no more than a given number of training vectors.

In the simplest case, we take a single pixel from a single multispectralimage of an unknown produce item. This vector is quantized, one bit at atime, by stepping through each level of the TSVQ. At each level, thecorresponding estimated distribution is used to estimate the probabilityof our item being a radish. Hopefully, with each succeeding level, thisestimated distribution will sharpen, so that we can gain certainty. Notethat if the TSVQ is designed exhaustively so that each leaf vector isassociated with exactly one training vector, the estimated distributionwill trivially identify the class of the nearest training vector. The“validity” of the estimated distribution hinges somewhat on the numberof training vectors it is based on. A powerful TSVQ classifier will tendto separate distributions several levels above the leaf nodes. FIGS.61-62 illustrate this with a hypothetical case of just two varieties,apples and bananas, and just two spectral dimensions. The example shownin FIG. 61 shows a strong classifier that separates the classes early inthe tree, and FIG. 62 shows a weak classifier.

To classify a single vector, the vector can be quantized to some desirednumber of levels within the tree, and the resulting estimateddistribution used to determine the class estimate. A simple method is tochoose the class with the highest probability (equivalently, choose theclass that had the most training vectors that quantized to the same codevector). If the training set distribution is a good representation ofthe “true” class distributions, this method is akin to maximumlikelihood estimation of the class.

Multi-Vector Classification

Of course, it is desirable to have more certainty than can be obtainedfrom classifying a single vector (pixel) from a multispectral image ofan unknown item. In general, multiple multispectral vectors can be usedto classify a single item. The simplest method might be to classify 5image pixels of the unknown item, and choose the mode as theclassification of the item. However, it may be useful to have the classestimate be a function of several estimated distributions, one for eachquantized vector. Such an approach would be to treat the five estimateddistributions as marginal from an independent joint probabilitydistribution. Combined with knowledge that each pixel observation isfrom the same (unknown) class, the resulting joint estimateddistribution is the product of the five marginal estimateddistributions, and choosing the maximum from among these is a reasonableclassification choice.

Distributional Approach

As more and more observations are made of an unknown item, we can beginto approximate the distribution of the item's spectricity. Now it makessense to ask which of the classes has a typical distribution that isclosest to the observed distribution of our unknown item. “Typicaldistribution,” here is used in an asymptotic equipartition propertysense. One possible approach is to use the Kullback-leibler divergenceas a distance measure between the observed distribution and thedistributions of the training vectors for each of the classes ofproduce. If the training set sizes for each class are equal, using theKullback-Leibler divergence is equivalent to choosing the class with themaximum sum of the logarithms of the estimated distributions.

Example implementations are provided in matlab source code fileappendices named ClassifierTSVQ_appendix.txt,basicClassify_appendix.txt, and VQ_appendix.txt.ClassifierTSVQ_appendix.txt includes code methods for training andclassifying a classifier. VQ_appendix.txt provides code for building anode of a tree of the VQ based classifier, and it is repeatedly invokedfor each node in the tree. basicClassify_appendix.txt includes code forcombining output of the classifier using multiplicative probability orKullback-Leibler approaches. This enables the classifier output fordistinct inputs to be combined in a manner that increases thediscriminating power of the system. For example, the classifier usesthis to combine the classifier output for several N-D spectricity pixelinputs taken from a suspect produce item that we wish to classify.Likewise, each input of the classifier may be a vector combining severalvectors into a single input vector. In this case, the classifier outputfor each such vector, itself a combination of vectors, may be combinedusing these techniques (multiplicative probability or Kullback-Leiblerapproaches).

b. Support Vector Machines (SVMs).

SVMs are a well-known machine learning technique. For background see: T.Fletcher, Support Vector Machines Explained, University College London,Mar. 1, 2009; C. Burges, A Tutorial on Support Vector Machines forPattern Recognition, Data Mining and Knowledge Discovery Volume 2 Issue2, June 1998, Pages 121-167, Kluwer Academic Publishers, which areincorporated by reference herein; and Support Vector Machine (andStatistical Learning Theory) Tutorial by Jason Weston of NEC LabsAmerica. As noted in the latter, SVM software is available from varioussources, e.g., LibSVM in C++, SVMLight, as well as machine learningtoolboxes that include SVMs: Torch (C++), Spider (MatLab), and Weka(Java), available at www.kernel-machines.org.

SVM is fundamentally a binary classifier. The simplest case of an SVMapplied to the apple dataset will handle single 45-dimensionalspectricity pixels. Classification among many classes proceeds through aseparate “one vs. rest” classifier for each of the classes to beidentified, with the class producing the highest output being chosen.

In the simplest case of a linear “kernel”, each spectricity vector inthe training set constitutes a single point in the training space. Thetraining process is a quadratic optimization problem that chooses theoptimum N-dimensional hyperplane to partition the classification choice.Typically at least two design parameters are manually optimized in theprocess as well. These parameters balance the degree of over/underfitting, and also the relative cost for misclassification vs. hyperplaneclassification margin distance.

The classification process takes an input spectricity value anddetermines on which side of the chosen hyperplane the input lies.

For some problems, a linear hyperplane might not do a good job ofseparating the raw spectricity values by class. In these cases, anonlinear kernel function can be chosen to see if the results can beimproved. The radial basis function (RBF), or Gaussian kernel is one ofthe most popular choices. When most kernel functions are used, the usualapproach is to increase the number of features (45 in this case for thelinear kernel) to be equal to the size of the training set. This resultsin a much slower training process for cases with large training sets.

One possible improvement to lower the complexity of nonlinear kernelSVMs would be to limit the expansion of the number of features to thenumber of voronoi cells in a VQ trained for the training setdistribution. Then the feature corresponding to a certain cell can becalculated as the sum of the features that would be calculated for eachtraining set member that is quantized to that voronoi cell.

A standard means of judging the degree of over/under fitting is to usen-fold cross validation to design classifiers using different trainingsets. The results can then be analyzed help determine the adequacy ofthe result.

There are two simple ways to accumulate classification results overmultiple spectricity pixels. The simplest is to sum up the “votes” forthe class of each pixel over all the pixels in a given unknown object,and choose the winning class. Another option is to use some weightedfunction of the directed distances of each spectricity pixel from thedecision hyperplane.

c. Neural Networks and associated learning methods (e.g., RNN,Refractory neural nets and vision) may also be applied to design anobject classifier for spectral vectors and spectral vectors combinedwith other features, 2D spatial or 3D spatial information associatedwith spectricity vectors.

For more information on learning methods and classification in spectralimaging, see, e.g., G. Camps-Valls, D. Tuia, L. Bruzzone, and J. A.Benediktsson, Advances in Hyperspectral Image Classification, IEEESignal Processing Magazine, Volume 31, Number 1, January 2014, pages45-54, which is hereby incorporated by reference. This article lists thefollowing approaches in the field of hyperspectral image classification,along with citations to publications corresponding to each one: kernelmethods and SVMs, sparse multinomial logistic regression, neuralnetworks, Bayesian approaches like relevance vector machines, andGaussian processes classification. It also lists spatial-spectralapproaches, and citations to publications corresponding to them.

Strategies for Dealing with Distributed Sources with Memory. There are avariety of methods to exploit the inter-pixel dependence to improveclassification results. All of these methods are highly sensitive toscale, in the sense that the joint distribution of two pixels in aspectricity image will naturally be a function of the distance betweenthose points on the object of interest.

Spectricity Texture. We experimented, and derived empirically, spectralimage based classifiers using a combination of spatial and spectralinformation. One category of approaches exploits the texture of groupsof spectricity pixels as a spatial metric of pixels leveraged incombination with spectral vectors for each pixel sampled from an object.Texture provides information about the spatial arrangement of these N-Dspectricity vectors in an image or selected region of an image. Texturemay be assessed using a variety of methods that make a quantitativemeasure of the arrangement of the spectral values of pixels in a region.Examples include edge based measures, e.g., based on edge magnitudeand/or direction of edges detected in a region. Related measures includeuse of a gradient based edge detector to detect edge metrics in a regionof pixels, such as gradient magnitude and direction, and then deriving atexture description by combining the edge metrics for the region. Onesuch approach is a histogram of the gradient magnitudes and orientationsof the region.

Co-occurrence matrices for the spectricity vectors of pixels in theregion are another example of texture measures for a region.

Texture masks convolved with a region are another way to measure variousspatial structures.

The use of spatial FFTs to derive spatial frequency characteristics ofthe N-D spectricity vector is yet another way to measure spatialrelationships among spectricity pixels.

Various spatial filtering techniques may be uses as well. Examplesinclude filters that compare each pixel with one or more neighboringpixels, or collectively, an average or other combination of spectralvectors of neighboring pixels. The spatial structure used fordetermining location or locations of pixels in a region for comparisonmay be empirically derived to detect particular structures forclassifying an object. For example, using matlab code, we derive atexture descriptor model in matlabe code that parameterizes therelationship between a pixel of interest and its neighbor or group ofneighbors in terms of relative location/spacing, direction, and functionfor comparison of the pixel and its neighbors (e.g., weighting appliedto the comparison as a function of pixel location to implement a filterfunction of a desired shape). The matlab code is a general filter modelwith adjustable parameters, where particular parameters create instancesof the filter that we can evaluate for effectiveness in our classifierfor a particular classification task. We then run experiments, pluggingin a range of different variables for use in our classifier to discoverthe variables that yield the most reliable classifier for the test dataset of the application.

One of skill will recognize that the various techniques, thoughdifferent in name, are seeking to exploit similar spatial structure orspatial relationships within a region of spectricity pixels.

Derivatives.

Continuing with this theme, we now describe a particular example wherewe leveraged spatial relationships between spectral values of pixels ina region to improve classification. In one embodiment, spectricityderivatives are input to the classifier, for training and forclassification. We experimented with various approaches in which theinput for training and testing the classifier comprised a summation ofspectricity vectors for pixels and spatial derivatives, generally of theform:

S+ΣS′+ΣS″+ . . . , where S is a spectricity vector at a pixel location,and S′ is a first derivative, S″ is a second derivative. For ourimplementation, our matlab software code computes the derivative asdifferences between the N-D spectricity value at the pixel location anda corresponding pixel location. We used a parameterized model assummarized above to test different relationships, varying the spacing,direction, and function for combining or not pixel values at two or morelocations prior to computing the difference between the combined valueand the value at the pixel of interest.

For the case of distinguishing apple varietals with our VQ classifier,we found that the spectricity difference values, computed at pixelspacing that corresponds to about 1-2 mm on the surface of the apple,provided improved discrimination accuracy over using spectricity valueswithout any spatial information as input to the VQ classifier. Inparticular, the matlab code computed pair wise spectricity differencesof a spectricity value of a brighter pixel minus the spectricity valueof a dimmer pixel approximately 4 pixels away, which in our spectralimage capture configuration corresponded to about 1-2 mm spacing on thesurface of the fruit. Of course, the parameters of the filter used tocompute a texture descriptor from spectricity vectors of pixels in aregion may vary by application, and can be derived using the empiricalmethod described or like methods. They may also be derived using machinelearning methods to ascertain values for parameters of the spectralbased texture descriptor that improves discrimination performancebetween classes. Other variations that may enhance performance include,but are not limited to:

-   -   Summation of derivatives over spatial scales (e.g.,        sub-millimeter, millimeter, centimeter spacing on the object        being imaged);    -   Including integrated brightness to the input data vector (less        as a discriminant, but more as way to determine and compensate        for measurement error)    -   Including spectricity or not in addition to the spectricity        difference as input to the classifier.

We sometimes refer to the spatial transform function of pixels prior toinputting to the classifier as a freckle transform, as it assists incharacterizing spatial structure/texture on the surface of the object.In particular, we observed that the spatial differencing was effectivein discriminating apple varietals with different surface texturecorresponding to freckle patterns.

The freckle transform may start out as a generalized spatial transformwith parameters that can be tuned to optimize the extraction of a vectorthat provides desired discrimination performance in the classifier.Indeed, the parameters of the transform can be tuned through machinelearning on a training set or sets of objects to be classified orrecognized.

Another observation is that the performance of the classifier can beenhanced by ascertaining variation in brightness across the N-D spectralmeasurements and compensating for that variation. This compensation isthen applied to input vectors prior to inputting them into theclassifier.

One particular method of classifying fruits and vegetables is asfollows:

sensing multispectral information from spaced-apart locations imagedfrom a vegetable or fruit;

determining multispectral differences between pairs of such locations;and

employing said multispectral differences, in conjunction with referencedata, in identifying the vegetable or fruit by cultivar.

Returning to the general topic of leveraging spatial relationships amongpixels, we emphasize that additional complementary forms of spatialstructure of a group of neighboring N-D spectricity pixels may be usedas well. Examples include multiresolution and rotation invariantmeasures of a texture feature of a neighborhood of spectricity pixels,such as texture derived from multiresolution analysis used in imageclassification. See for example, US Patent Publication 20030147558.Multiresolution analysis methods include wavelet and Gabor transformbased methods. Rotation invariant texture may also be used, such asrotation invariant methods employing Radon transforms.

Classifying Vectors of Spectricity Pixels. By classifying multiplespectricity pixels in a single feature vector, the joint probabilitydistribution over the multiple pixels is used for the classifier design,and so the conditional distributions on one pixel given other pixels canbe taken advantage of. Classifying vectors of pixels together isfundamentally similar to the common practice in image and videocompression of quantizing groups of pixels to take advantage of thememory in the source.

All else being equal, the classification task for groups of pixels willrequire a larger training set to adequately fit the joint distribution,and will, unsurprisingly, be more complex.

To capture the largest amount of memory for a given size vector, it isreasonable to choose pixels close together (under the assumption thatnearby locations are more correlated than farther apart locations); acommon choice would be to choose a vector of n×n spectricity imagepixels.

Both VQ based approaches and SVM can be used to classify vectors ofpixels.

In the case of a VQ based system, the estimated pmfs would be over ak-dimensional product space of the VQ cell indexes, where k is thenumber of pixels in each vector to be quantized. This would likely beimpractical for all but the smallest sized vectors. One approach tomitigate the complexity would be to use a VQ with a smaller number ofcells.

For SVM, complexity will also increase with vector dimension, butprobably not as quickly as with the VQ approach. Also, there is aspecific kernel, called histogram intersection, which has beensuccessfully used for images, and which can be efficiently calculated.

Multiscale Classification

Resampling the image (such as by using an averaging filter) at differentscales, might produce different spectricity distributions for differentscales. These differences can be another method for differentiatingbetween classes. This method is attractive because it would not greatlyincrease complexity (probably nearly linear in the number of scales).Both VQ based methods and SVM methods could be used.

Crowd Sourcing to Compile Reference Data of Spectral Images and ObjectLabels

One practical challenge in building and maintaining classifiers is thecollection, enrollment and accurate labeling of reference featurevectors sets captured for particular classes of objects. The techniquesdescribed in this document facilitate crowd based sourcing of spectralimages. One way they facilitate it is by providing a means tocharacterize the light source and camera configuration of user'sdevices, such as by calibrating based on a device's coupling matrix.This simplifies the user contribution, as they can simply identify acamera device or smartphone used to capture uploaded image data, and thecloud service, in turn, applies the corresponding calibration by lookingup the coupling matrix for the device and applying it to the uploadedimage content. This calibration process can be automated through ahandshake process between the user's mobile device and cloud service:upon establishing a communication with the spectral image enrollmentserver in the cloud, the user's device shares its camera deviceparameters. The enrollment server, in response, retrieves a couplingmatrix corresponding to the camera device parameters (e.g., whichidentifies make, model of smartphone and/or its version of light sourceand camera sensor pairing.) The spectral data uploaded is thentransformed according to the coupling matrix to calibrate it with otherreference spectral vectors enrolled in the reference database ofspectral vector images.

Surface Morphology

We noticed in spectral images obtained for a collection of greenvegetables and peppers in the camera's field of view that spectricitysignature values seem to have very distinct ridging and contouringaround the various subject matter, with the Zucchini and Cucumbers beingparticularly striking in this regard. Part of this effect may be due toslight non-linear residual properties of the camera, where surfaceshaving different slant-angles relative to the camera will move throughluminance space and ever so lightly change the ratios of LED/pixeldigital values (hence, slightly change the ˜8-12D vector values). Sothis ‘problem’ with a slightly non-linear camera (which almost allcameras are not perfectly linear) now provides a way to measure surfacenormal, and recover an estimate of 3D shape, as disclosed herein.

Back Projecting Approaches to RGB Cameras

Several of the approaches discovered in our experiments have utility inthe 2D chromaticity space. In particular, while using multiple LEDsprovides advantages, in some cases, our inventive methods andconfigurations can be implemented using Bayer color cameras and signalprocessing of the chromaticity images captured from them. Ourmethodology for deriving these methods is as follows: develop a signalprocessing method using a higher dimensional space (e.g., 6D-15Dspectricity ratios), and then seek to approach similar results in the 2Dchromaticity space (e.g., 2 chromaticity ratios). One example is theabove mentioned process of determining shape from chromaticitygradients.

Spectral Imaging Integrated with Other Recognition Technologies

Object Recognition Combining Spectral Image Based Recognition with OtherFeature Vectors

As described above, the above techniques for capturing and derivingspectral based feature vectors can be combined with 2D and 3Drecognition methods to improve object discrimination and identification.The following sections, and material incorporated by reference, provideadditional explanation of such recognition methods, as adapted toleverage spectral image information for identification.

In one embodiment, object recognition is enhanced by performing locallyadaptive combination of spectral images (e.g., 15D spectricity vectors)to extract black/white images that are then input to 2D imagerecognition methods. Many image recognition techniques predominantlyrely on spatial features and structures derived from luminance images(black and white images), neglecting color and spectral information forobject discrimination and recognition. These spatial features includesize and shape of structures in an image, often characterized bycontours, edges or corners.

Machine learning techniques can be employed to derive a mapping of N-Dspectral vectors to images that provide more reliable discrimination ofimages, and objects depicted within the images. Once derived, themapping is applied to generate 2D images that are fed to the 2D or 3Drecognition services for identification.

One such example is the use of a mapping of the N-D spectral vectors toa spectral feature set to provide a substitute for color based featurevectors in a Bag of Features image or object recognition approach.Various techniques described in this document or the referencesincorporated herein may be used to derive the mapping of N-D spectralvector images to a spectral feature vector for such applications.

One example employing vector quantization and Bag of Features is asfollows. In a Bag of features approach for object recognition based onimage input, the input image data undergoes:

1. Feature Extraction in which the input images are converted to sets ofdescriptors of various types, which may include SIFT, dense,color-based, shape based, and N-D spectral based descriptors;

2. Quantization: for each set of feature descriptors, quantize the setinto quantization bins. There are a variety of strategies for assigningdescriptors to bins, as noted in connection with vector quantization.Such strategies include K-means, soft assignment, e.g., Gaussianmixture, etc. The process of assigning descriptors to bins results in ahistogram, which provides a frequency of mapping descriptors into binsfor a particular descriptor type. The histograms provide arepresentation of an unknown input that can then be matched against adatabase of reference histograms for identification (e.g., looking upthe closest match, and determining the unknown item to have the identityor classification of that matching reference item).

3. The above methodology provides a basis for automated classifierdesign, or machine learning. For example, a neural net methodology hasinputs for the bins of the histograms. It can be trained by submittinglabeled items, e.g., objects.

N-D spectral vectors provide a powerful discriminator and identifier inthis type of frame work. It may be employed for object recognition,image recognition and related classification applications. Below, weprovide additional background on methods in which the spectralinformation may be employed as a feature descriptor.

Background for Image Recognition

Fingerprint-based content identification techniques are well known.SIFT, SURF, ORB and CONGAS are some of the most popular algorithms.(SIFT, SURF and ORB are each implemented in the popular OpenCV softwarelibrary, e.g., version 2.3.1. CONGAS is used by Google Goggles for thatproduct's image recognition service, and is detailed, e.g., in Neven etal, “Image Recognition with an Adiabatic Quantum Computer I. Mapping toQuadratic Unconstrained Binary Optimization,” Arxiv preprintarXiv:0804.4457, 2008.)

Still other fingerprinting techniques are detailed in patentpublications 20090282025, 20060104598, WO2012004626 and WO2012156774(all by LTU Technologies of France).

Yet other fingerprinting techniques are variously known as Bag ofFeatures, or Bag of Words, methods. Such methods extract local featuresfrom patches of an image (e.g., SIFT points), and automatically clusterthe features into N groups (e.g., 168 groups)—each corresponding to aprototypical local feature. A vector of occurrence counts of each of thegroups (i.e., a histogram) is then determined, and serves as a referencesignature for the image. To determine if a query image matches thereference image, local features are again extracted from patches of theimage, and assigned to one of the earlier-defined N-groups (e.g., basedon a distance measure from the corresponding prototypical localfeatures). A vector occurrence count is again made, and checked forcorrelation with the reference signature. Further information isdetailed, e.g., in Nowak, et al, Sampling strategies for bag-of-featuresimage classification, Computer Vision—ECCV 2006, Springer BerlinHeidelberg, pp. 490-503; and Fei-Fei et al, A Bayesian HierarchicalModel for Learning Natural Scene Categories, IEEE Conference on ComputerVision and Pattern Recognition, 2005; and references cited in suchpapers.

Background on 3D Object Recognition

In our related work, we describe methods for 3D object recognition basedon capture of 2D images. See our related application 61/838,165,entitled ID of Things, which is hereby incorporated by reference.

In addition to this work, several papers outline methods for 3D objectrecognition, and are incorporated by reference herein. The objectrecognition techniques in the following can be adapted by using spectralimage data as input and additionally employing spectral signatures forobject discrimination:

-   -   Fei-Fei et al, A Bayesian Hierarchical Model for Learning        Natural Scene Categories, IEEE Conference on Computer Vision and        Pattern Recognition, 2005;    -   Ohbuchi, et al, Distance Metric Learning and Feature Combination        for Shape-Based 3D Model Retrieval, Poster Presentation, Proc.        of the ACM workshop on 3D Object Retrieval, 2010.    -   Lian, et al, Visual similarity based 3D shape retrieval using        bag-of-features, IEEE Shape Modeling International Conference        2010; and    -   Ohbuchi, et al, Accelerating bag-of-features SIFT algorithm for        3d model retrieval, Proc. SAMT 2008 Workshop on Semantic 3D        Media; which are all hereby incorporated by reference.

These techniques are made more powerful by utilizing a mapping of N-Dspectral vectors into spectral signatures as a means to furtherdiscriminate objects. In addition, the N-D spectral vectors are mappedinto color or black and white images that are used for featureextraction as a substitute for the feature extraction from image inputused previously in these methods.

Imaging devices with 3D sensing capability, such as plenoptic camerasand Kinect sensors provide the capability of shape of 3D objects to beascertained and added as a discriminating or identifying feature inputto a classifier or recognition system. These varying types of 3Dinformation, including 3D information to obtain 3D surface texture and3D information to determine object shape and boundaries can also beleveraged with the other technologies described in this document toclassify and recognize objects.

Produce (e.g., Fruit and Vegetables)

In commonly assigned provisional application 61/724,854, we disclose amethod of gathering spectral signature for incoming batches of fruit asit arrives at a grocery store, and using this batch-derived signatureinfo (rather than a worldwide “Standard” for fruit signature data) forfruit identification. 61/724,854, and US Patent Application Publication20130223673, both entitled METHODS AND ARRANGEMENTS FOR IDENTIFYINGOBJECTS, which are hereby incorporated by reference.

As noted above, others have posited that spectral information can beused for produce identification at check-out. See Henty's U.S. Pat. Nos.6,363,366 and 7,319,990, which are hereby incorporated by reference.

In this section, we describe a produce classifier based on the abovespectral imaging technology. A first embodiment utilizes 7 narrow-bandLEDs and a color video camera capture. Another embodiment is the same,but uses a black and white video camera.

The LED lighting and the camera view are co-centered on a point on aconveyor belt. The LED lighting is cycled, (1 to 2 full cycles persecond) such that there are individual full frames inside the videostream which uniquely correspond to only one LED source being on duringthat full frame's exposure. Compiled Matlab code ingests the video,picks out these uniquely lit frames, and quickly generates an N-D (N isempirically derived) spectricity signature vector for every point in thecamera's field of view. The code also has access to a library offruit/vegetable N-D signature families—essentially average N-Dsignatures for unique kinds of fruits/vegetables. Software code thencompares acquired N-D scene signature vectors with this stored library,and when the acquired signature is within a threshold of proximity to alibrary signature, an output value for that pixel will be generatedcorresponding to the matched fruit/vegetable. Such output values,ranging across several types of fruits/vegetables, can then be ‘mixed’with the ingest video to then produce a graphic ID-overlay video stream.

As additional background for the use of spectral information for produceidentification and ripeness, see: A. Solovchenko, O. Chivkunova, A.Gitelson, and M. Merzlyak, Non-Destructive Estimation of PigmentContent, Ripening, Quality and Damage in Apple Fruit with SpectralReflectance in the Visible Range, in Fresh Produce 4 (Special Issue 1),91-102 © 2010 Global Science Books, which is hereby incorporated byreference. On page 4, second column mid-way down, this article refers tosignature analysis of fruit spectra′ and refers to three key wavelengthsas the ratio generators. This provides background as to the use ofspectral information to discriminate fruit/produce and relativeripeness. Our technology enhances identification and discriminationusing readily available light source and camera components, configuredas described, to generate spectral images. Selection of the LED spectrais guided by which chemical species are involved in the subject matter,mainly chlorophyll, carotenoid, etc.

Ripeness

Building on this background, FIGS. 58-60 illustrate an application ofN-D spectral vectors to identify ripeness of produce. In thisapplication, the spectral characteristics of a produce item arecharacterized in N-D spectral space. As illustrated, a produce itemfollows a path or curvature through N-D space that is correlated to itsstage of ripeness, and also accounts for pick date and time elapsedsince the pick date. Unique models defining these regions for variousproduce items are derived through a training process on sets of spectralimages collected for the produce items.

To determine ripeness, the produce item is imaged using spectral imagecapture techniques described above and spectral vectors are derived andmapped into the N-D space. The mapped data is correlated with the modelto determine where it is located along the ripeness path. This ripenessdetermination is then output. One form of output, for example, is an ARtype UI as explained above, in which the user's mobile device displays agraphic overlay on the video feed of a produce item depicting its stageof ripeness.

As noted above, 2D, 3D spatial information combined with spectral andpolarimetric information at or below the surface of a produce timeprovide additional discrimination of produce type and ripeness. Wecombine the above described imaging devices for capturing polarimetricand spectral information at or below an object's surface with machinelearning based design of a classifier to discern produce type andripeness. Our design of such systems draws on work in fields of spectralimaging, stereochemistry, and ellipsometry. The fields of phytochemistryand biochemistry also provides useful teaching regarding therelationship of optical properties and produce classification andripeness, as noted above, and in the cited work by Solovchenko et al.See also, K. Gross; C. Sams, Changes in Cell Wall Neutral SugarComposition During Fruit Ripening: a species survey, Phytochemistry,Volume 23, Issue 11, 1984, Pages 2457-2461, which is hereby incorporatedby reference. This work analyzing changes in sugar molecule compositionduring ripening indicates that measurements of the composition byoptical means provides an indicator of ripeness stage. Thus, the abovedescribed spectral image capture and measurement of polarimetricinformation corresponding to sugar composition at or just below thesurface of produce provides an indicator of ripeness. The abovetechniques for designing classifiers for such features, therefore,provide guidance for building ripeness classifiers for produce items.Specifically, in one configuration, spectricity vectors, possibly incombination with spatial and polarimetric information, are input into aclassifier to discern produce type. Then in another classifier stage,optical measures of ripeness are input to a classifier to ascertainripeness stage for that produce type. Various configurations arepossible. In some applications, the user may simply select the producetype, and then use the classifier to compute the ripeness stage fromoptical information captured from the produce item.

Recapping the above themes on produce classification and ripeness stagedetection, the task of distinguishing one fruit/vegetable from another,followed by identification of the ‘ripeness stage’ that a given produceitem is in, has many underlying physical bases to draw from, not justthe pigment molecule presents itself on the surface of a particularproduce item. The processes going on underneath the top expressedsurface layers are important to the ripeness-stage expressions of thesurface in the surface's full three dimensionality. This underlyingcell-structure development also gives rise to characteristicspatial-scale patterning of those structures, some at the sub-millimeterdominant scale and others a sub-centimeter scales and larger, fitting inwell to sampling of spatial information at a range of spatial scales anddepths.

The above techniques can be applied similarly to many applicationsspaces, including color matching for cosmetics (matching make-up to skintones), color matching for paints and inks, automated printer colorcalibration, and spectral analysis of blood for various health analyticapplications. These are just a few examples. The wider array ofapplications based on spectroscopic technology are applications wherethis technology may be applied to provide advances in terms of cost,effectives, and wider deployment. As the above technology relies onlight source and camera sensor pairs that are readily available in manyform factors, including for mobile and wearable computers and sensors,the technology can extend spectral imaging applications across a widerarray of devices and form factors.

Personal Health and Nutrition

One growing trend is the development of wearable health monitoringdevices, such as bracelets, with sensors to track motion, etc. The abovetechnology may be integrated into this wearable form factor to capturespectral image data of blood flowing beneath the skin where the deviceis worn by a user. As the user's body breaks down food, the LED-camerabased sensor detects the amount of light that passes through the bloodbased on green, red and infrared patterns.

Unique Identification of Printed Objects

The identification power of N-D spectral vectors may be leveraged byselecting combinations of inks or ink additives that uniquely identifyor discriminate classes of printed objects. Patches of such unique inkformulations may be printed on product packaging for example, toidentify it. The use of ink variations, as well as the spatial dimensionto vary formulations over different patches, provides additional degreesof freedom to identify a printed item (as a function of spectralcomposition and location to provide a 2D or higher dimensional spectralcode as function of location and N-D spectral vector composition). Thisapplication of spectral codes may also be applied in layers applied by3D printers.

These objects are identified by computing spectral N-D vector imagesfrom images captured of the printed object, mapping them to a featuredescriptor space, and matching them with reference data in a referencedatabase (using above referenced classification technologies, forexample). Alternatively, or in combination, the spectral descriptors maybe used to encode data symbols, which are detected using a classifier,then converted to a data symbol and further processed (e.g., using errorcorrection and detection) to provide a robust, variable data signal thatcan encode an identifier and any other desired metadata.

The standard Pantone spot color set consists of 1114 different spotcolors, each mixed from some combination of 13 base inks, plus black. Ofthese, somewhat over 50% of them can be matched by screening acombination of the standard CMYK process inks. Pantone has a 6 colorprocess, called Hexachrome, which allows screened reproduction of almost90% of the spot colors. So, one can get around 8 or 9 bits per screenedCMYK color “patch”, and slightly more for a Hexachrome “patch”. Theselection of inks may be designed in conjunction with the selection ofthe LED sensor pairing of a reader device to obtain the desired addressspace of unique symbols that may be encoded in a particular printedpatch.

As another variation, optical nanodot solutions can be added to inkformulations to introduce spectrally distinguishable characteristics.For example, differing ratios of nanodot injected material produces amodulation of the spectral vector of a printed patch, which can be usedto encode a data symbol or graphical element of a detectable geometricpattern.

Relatedly, digital watermarks may be encoded in spectral information asdisclosed in our related application 61/832,752, which is incorporatedby reference. See also teaching of additional signal encoding techniquesin 61/832,752, which is also incorporated by reference. The teachings of61/832,752 and 61/832,752, can be combined with the technologies in thisdisclosure to provide a means to identify printed objects using variousdata encoding techniques, identifying patterns, image recognition inspectral domains, including spectral ratio or spectral differences, asdisclosed in these references and this document.

This technology can then be applied in various other industries wheresuch spectral information may be conveyed in colorants, dyes, inks etc.,such as food dyes, clothing dyes, colorants for cosmetics,pharmaceuticals, medical diagnostic materials for imaging within thehuman body, etc.

Regarding medical imaging applications, our techniques of using spectralinformation, alone or in combination polarimetric information and 2D and3D spatial, depth (e.g., spectral and polarimetric measurements forpixels at and below skin surface), and can be used to augment approachessuch as described in U.S. Pat. Nos. 6,996,549 and 8,543,519, which arehereby incorporated by reference.

Other Form Factors

Point of Sale Form Factors

Another important form factor is object scanning equipment at the Pointof Sale (POS). Barcode scanning equipment increasingly employs digitalcameras to capture images of objects as they are waved passed a scanner.This equipment is a suitable environment in which light source—camerasensor pairs may be employed as disclosed above. It affords theadvantage of positioning light sources and cameras to measure spectralinformation, as well as derive surface structure information asdescribed.

Additional Applications

The following table provides additional application fields, use casesand example spectral imaging configurations employing technologydescribed in this document. The additional product details are examplesonly and any of the device types noted in the document may be employed,as appropriate for the application.

APPLICATION Explanation Additional Product Details Digital A naturalfit, see above Smartphone, POS scanner, watermarking special purposeimager Quality Control excellent fit - use N++ band In machine visionequipment in (UV/IR) manufacturing setting; and post shipping, insmartphone embodiments Dermatology Identify skin problems withstandalone camera UV, IR Dental Use your camera phone to Integrated insmartphone check for plaque Security Camera IR LED, big marketIntegrated in security camera CPG - checkout Improved barcode, digitalIntegrated in POS imager watermark on packaging improved using spectralchannel Part Inspection Identify specific appearance In machine visionequipment in aspects manufacturing setting Fruit/Vegetable UV, IR and‘yellow’ - beats Integrated in POS imager or in- human eye store producescale, or machine vision system of produce supply chain Socialinteraction like pheromones but with mood analyzer in smartphone colorapplication Art Photography/ Special effects like IR better color,pseudocolor, with Graphics images specialty flash and software/firmware,FPGA, and/or ASIC in camera Professional Enhanced color rendition samePhotography Consumer Always a good picture with same photographyimproved ambient sensing of lighting on subject and adapt flash ArchivalEnhanced color rendition photography Counterfeit Great application, goodfit Spectral information provides detection greater discrimination ofcounterfeits Medical Many applications Stress Test Blood flow inforehead? IR Breathalyzer UV/IR can ‘see’ chemistry in vaporSpelunking/Mining High value niche Optometry Inspect white of eye MotionPicture Cinematography; DDX Endoscopy Agriculture fluoresence - UVespecially looking at cultures/nurseries/ and possibly IR Healthy?Flowering? Forensics Crime scene, lit by UV to every department needsone/ see DNA DDX + special camera BioTech fluoresence - UV especiallyMicroscope, DDX Traffic Cam IR of course Shoe Sales Paint store Needhigh accuracy Use spectrometer Fabric store Need high accuracy Tailor'sshop Hair Salon Possibly easy, good size market Science teaching Easyphilanthropy Sports Photography (training facility) high frame rateflash (pro vs everyone else?) Surveillance IR in the dark of course, butwhat's the benefit N++? Crime Prevention tracking? Lighting of largearea? Facial Recognition Underwater Photography Chemical compositionBlood donor Passport Watermark reading and photography documentauthentication Airline check-in Watermark reading and documentauthentication Ticket gate Watermark reading and document authenticationCrowd counter War games Minerals evaluation Oil and gas explorationLicense plate capture All the lightbulbs in the factory areWhite/White - time alternated colorations generated from pulsingdifferent spectral LEDs, for example. Consumer-use Inspection of fruit,merchandise, fabricConcluding Remarks

Applicant's other work concerning imaging systems is detailed, e.g., inpatent publications 20110212717, 20110161076, 20120284012, 20120218444,20120046071, and in application Ser. No. 13/750,752, filed Jan. 25, 2013(Now issued as U.S. Pat. No. 9,367,770), and 61/759,996, filed Feb. 1,2013.

Chrominance-based digital watermarking is detailed, e.g., in thejust-cited application Ser. No. 13/750,752, and in U.S. patent documents20100150434, U.S. Pat. Nos. 6,590,996 and 8,401,224.

While reference has been made to smart phones, it will be recognizedthat this technology finds utility with all manner of devices—bothportable and fixed. Tablets, laptop computers, digital cameras, wrist-and head-mounted systems and other wearable devices, etc., can all makeuse of the principles detailed herein. (The term “smart phone” should beconstrued herein to encompass all such devices, even those that are nottelephones.)

Particularly contemplated smart phones include the Apple iPhone 5; smartphones following Google's Android specification (e.g., the Galaxy S IIIphone, manufactured by Samsung, the Motorola Droid Razr HD Maxx phone,and the Nokia N900), and Windows 8 mobile phones (e.g., the Nokia Lumia920).

Among the Android options, the Nokia N900 is usable with the open sourceFCam software for programmatic computer camera control. This isadvantageous because the FCam technology can be called to cause a cameratake certain actions that might be useful in a particular analysis.

Details of the Apple iPhone, including its touch interface, are providedin Apple's published patent application 20080174570.

The design of smart phones and other computers referenced in thisdisclosure is familiar to the artisan. In general terms, each includesone or more processors, one or more memories (e.g. RAM), storage (e.g.,a disk or flash memory), a user interface (which may include, e.g., akeypad, a TFT LCD or OLED display screen, touch or other gesturesensors, a camera or other optical sensor, a compass sensor, a 3Dmagnetometer, a 3-axis accelerometer, a 3-axis gyroscope, one or moremicrophones, etc., together with software instructions for providing agraphical user interface), interconnections between these elements(e.g., buses), and an interface for communicating with other devices(which may be wireless, such as GSM, 3G, 4G, CDMA, WiFi, WiMax, Zigbeeor Bluetooth, and/or wired, such as through an Ethernet local areanetwork, a T-1 internet connection, etc.).

The processes and system components detailed in this specification maybe implemented as instructions for computing devices, including generalpurpose processor instructions for a variety of programmable processors,including microprocessors (e.g., the Intel Atom, ARM A5, and nVidiaTegra 4; the latter includes a CPU, a GPU, and nVidia's Chimeracomputational photography architecture), graphics processing units(GPUs, such as the nVidia Tegra APX 2600), and digital signal processors(e.g., the Texas Instruments TMS320 and OMAP series devices), etc. Theseinstructions may be implemented as software, firmware, etc. Theseinstructions can also be implemented in various forms of processorcircuitry, including programmable logic devices, field programmable gatearrays (e.g., the Xilinx Virtex series devices), field programmableobject arrays, and application specific circuits—including digital,analog and mixed analog/digital circuitry. Execution of the instructionscan be distributed among processors and/or made parallel acrossprocessors within a device or across a network of devices. Processing ofdata may also be distributed among different processor and memorydevices. As noted, cloud computing resources can be used as well.References to “processors,” “modules” or “components” should beunderstood to refer to functionality, rather than requiring a particularform of implementation.

Software instructions for implementing the detailed functionality can beauthored by artisans without undue experimentation from the descriptionsprovided herein, e.g., written in C, C++, Visual Basic, Java, Python,Tcl, Perl, Scheme, Ruby, etc. Smartphones and other devices according tocertain implementations of the present technology can include softwaremodules for performing the different functions and acts.

Known browser software, communications software, imaging software, andmedia processing software can be adapted for use in implementing thepresent technology.

Software and hardware configuration data/instructions are commonlystored as instructions in one or more data structures conveyed bytangible media, such as magnetic or optical discs, memory cards, ROM,etc., which may be accessed across a network. Some embodiments may beimplemented as embedded systems—special purpose computer systems inwhich operating system software and application software areindistinguishable to the user (e.g., as is commonly the case in basiccell phones). The functionality detailed in this specification can beimplemented in operating system software, application software and/or asembedded system software.

Different of the functionality can be implemented on different devices.Thus, it should be understood that description of an operation as beingperformed by a particular device (e.g., a smart phone) is not limitingbut exemplary; performance of the operation by another device (e.g., aremote server), or shared between devices, is also expresslycontemplated.

(In like fashion, description of data being stored on a particulardevice is also exemplary; data can be stored anywhere: local device,remote device, in the cloud, distributed, etc.)

This specification has discussed several different embodiments. Itshould be understood that the methods, elements and concepts detailed inconnection with one embodiment can be combined with the methods,elements and concepts detailed in connection with other embodiments.While some such arrangements have been particularly described, many havenot—due to the large number of permutations and combinations. However,implementation of all such combinations is straightforward to theartisan from the provided teachings.

Elements and teachings within the different embodiments disclosed in thepresent specification are also meant to be exchanged and combined.

While this disclosure has detailed particular ordering of acts andparticular combinations of elements, it will be recognized that othercontemplated methods may re-order acts (possibly omitting some andadding others), and other contemplated combinations may omit someelements and add others, etc.

Although disclosed as complete systems, sub-combinations of the detailedarrangements are also separately contemplated (e.g., omitting various ofthe features of a complete system).

While certain aspects of the technology have been described by referenceto illustrative methods, it will be recognized that apparatusesconfigured to perform the acts of such methods are also contemplated aspart of applicant's inventive work. Likewise, other aspects have beendescribed by reference to illustrative apparatus, and the methodologyperformed by such apparatus is likewise within the scope of the presenttechnology. Still further, tangible computer readable media containinginstructions for configuring a processor or other programmable system toperform such methods is also expressly contemplated.

The present specification should be read in the context of the citedreferences. (The reader is presumed to be familiar with such priorwork.) Those references disclose technologies and teachings that theinventors intend be incorporated into embodiments of the presenttechnology, and into which the technologies and teachings detailedherein be incorporated.

To provide a comprehensive disclosure, while complying with thestatutory requirement of conciseness, applicantincorporates-by-reference each of the documents referenced herein. (Suchmaterials are incorporated in their entireties, even if cited above inconnection with specific of their teachings.)

In view of the wide variety of embodiments to which the principles andfeatures discussed above can be applied, it should be apparent that thedetailed embodiments are illustrative only, and should not be taken aslimiting the scope of the invention. Rather, we claim as our inventionall such modifications as may come within the scope and spirit of thefollowing claims and equivalents thereof.

The invention claimed is:
 1. An apparatus for spectral imagingcomprising: a color image sensor operable to obtain color images,comprising R, G and B color components, the color images comprisingpixel values corresponding to locations in a field of view of the colorimage sensor; an illumination source comprising at least four LEDs, eacha different color; a drive circuit that selectively strobes on the fourLEDs synchronized with capture of frames of the color images by thecolor image sensor; a memory comprising instructions; and a processor,configured to execute instructions from the memory to apply a couplingfactor to pixel values of the color images corresponding to a spectralchannel to provide spectral channel values, wherein a spectral channelis associated with a combination of color of the illumination source anda color component of the color image sensor; the processor configured toexecute instructions from the memory to sum pixel values forcorresponding locations to provide sums for the corresponding locations,and the processor configured to execute instructions from the memory tocompute a ratio of the spectral channel value and sum of a correspondinglocation to provide a spectricity vector for the corresponding location.2. The apparatus of claim 1 wherein the drive circuit strobes off theillumination source in synchronization with capture of a color image bythe color image sensor to obtain a reference image of ambient lightwithout illumination by the LEDs, and the processor is configured toexecute instructions to subtract pixel values of the reference imagefrom pixel values of a color image obtained under illumination of an LEDlight source.
 3. The apparatus of claim 1 wherein the processor isconfigured to execute instructions to reverse gamma from the colorimages prior to applying the coupling factor.
 4. The apparatus of claim1 wherein the processor is configured to execute instructions of atrained classifier and is configured to execute instructions to computea spatial relationship function of pixels sampled from differentlocations of a scene to obtain a vector of multi-spectral channels perpixel and spatial relationships among the pixels, and the processor isconfigured to execute instructions of the trained classifier on thevector to classify an object depicted in the color images as being oneof plural different classes that the trained classifier is trained torecognize.
 5. The apparatus of claim 4 wherein the processor isconfigured to execute instructions from the memory to apply theclassifier to the vector to classify a produce item in the scene.
 6. Theapparatus of claim 4 wherein the spatial relationship function comprisesa function of multi-spectral values of pixels at 2 or more spatialdimensions.
 7. The apparatus of claim 6 wherein the spatial relationshipfunction comprises a function of multi-spectral values of pixels at 3 ormore spatial dimensions.
 8. The apparatus of claim 7, wherein the colorimage sensor comprises a polarimetric sensor that provides polarimetricinformation from a produce item; and wherein the processor is configuredto execute instructions to compute a function of polarimetricinformation and spectral information to produce a polarimetric dependentvector; and the processor is configured to execute instructions of thetrained classifier to classify the produce item based on thepolarimetric dependent vector.
 9. An apparatus for spectral imagingcomprising: an image sensor operable to obtain images, the imagescomprising pixel values corresponding to locations in a field of view ofthe image sensor; an illumination source comprising at least four LEDs,each a different color; a drive circuit that selectively strobes on thefour LEDs synchronized with capture of frames of the images by the imagesensor; a memory comprising instructions; and a processor, configured toexecute instructions from the memory to obtain images corresponding to aspectral channel to provide spectral channel values, wherein a spectralchannel is associated with a color of the illumination source; theprocessor configured to execute instructions from the memory to sumpixel values for corresponding locations to provide sums for thecorresponding locations, and the processor configured to executeinstructions from the memory to compute a ratio of the spectral channelvalue and sum of a corresponding location to provide a spectricityvector for the corresponding location.
 10. The apparatus of claim 9wherein the processor is configured to execute instructions of a trainedclassifier and is configured to execute instructions to compute aspatial relationship function of pixels sampled from different locationsof a scene to obtain a vector of multi-spectral channels per pixel andspatial relationships among the pixels, and the processor is configuredto execute instructions of the trained classifier on the vector toclassify an object depicted in the images as being one of pluraldifferent classes that the trained classifier is trained to recognize.11. The apparatus of claim 10 wherein the scene comprises a produceitem, and the processor is configured to execute instructions from thememory to apply the classifier to the vector to classify the produceitem.
 12. The apparatus of claim 10 wherein the spatial relationshipfunction comprises a function of multi-spectral values of pixels at 2 ormore spatial dimensions.
 13. The apparatus of claim 12 wherein thespatial relationship function comprises a function of multi-spectralvalues of pixels at 3 or more spatial dimensions.
 14. The apparatus ofclaim 1, wherein the image sensor comprises a polarimetric sensor thatprovides polarimetric information from a produce item; and wherein theprocessor is configured to execute instructions to compute a function ofpolarimetric information and spectral information to produce apolarimetric dependent vector; and the processor is configured toexecute instructions of the trained classifier to classify the produceitem based on the polarimetric dependent vector.
 15. A non-transitorycomputer readable medium on which is stored instructions, theinstructions, when executed by a computer, are configured to perform amethod of spectral imaging comprising: obtaining color images through asensor, comprising R, G and B color components, the color imagescomprising pixel values corresponding to locations in a field of view ofthe sensor, and being captured during corresponding illumination periodsin which different LED light sources illuminate the field of view of thesensor; applying a coupling factor to pixel values of the color imagescorresponding to a spectral channel to provide spectral channel values,wherein the spectral channel is associated with a combination of lightsource and a color component; summing pixel values for correspondinglocations to provide sums for the corresponding locations; and for Nspectral channels and the locations, computing a ratio of the spectralchannel value and sum of a corresponding location to provide aspectricity vector for the corresponding location.
 16. Thenon-transitory computer readable medium of claim 15 wherein theinstructions are further configured to obtain a reference image ofambient light without illumination by the LED light sources, and tosubtract pixel values of the reference image from pixel values of acolor image obtained under illumination of an LED light source.
 17. Thenon-transitory computer readable medium of claim 15 wherein theinstructions are further configured to reverse gamma from the colorimages prior to applying the coupling factor.
 18. The non-transitorycomputer readable medium of claim 15 wherein the instructions arefurther configured to determine a spatial relationship function ofpixels sampled from different locations of a scene to obtain a vector ofmulti-spectral channels per pixel and spatial relationships among thepixels, and to input the vector to a classifier, the classifier beingtrained to distinguish between classes of objects based on a vector ofmulti-spectral channels per pixel and spatial relationships among pixelsof spectral images.
 19. The non-transitory computer readable medium ofclaim 18 comprising instructions configured to apply the classifier tothe vector to classify a produce item in the scene.
 20. Thenon-transitory computer readable medium of claim 19 comprisinginstructions configured to determine the spatial relationship functionfrom multi-spectral values of pixels at 2 or more spatial dimensions.